Help, reduced engine power
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
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Help, reduced engine power
After driving 1 hour on the highway my car's dash message was reduced engine power and service active handling. I could not get the engine to rev over 1 k rpm's. I turned off the car and restarted and then there's no more messages on the dash and the car runs great for 2-3 minutes and then goes back into the reduced engine power mode. Car is 2003 Z06 with p1 procharger installed by andy at A & A in 2005. Car has never had a problem until 3 weeks ago when I got caught in a monsoon rain and I was at a red light when a 18 wheel truck came and created a tidal wave into my car and I put it into gear to try to move and the engine stalled and had to be towed. Water had gotten all the way into the intake manifold and the spark plugs were taken out and water was coming out of the spark plug holes. Everything was dried out and new plugs and wires were placed and the car ran great until today. I cleared the codes and the only 2 codes now are P1515 H C (Command vs Actual throttle perfomance (pcm module)) and
C1278 H (temporarily inhibited by pcm). I
assume that the pcm also got wet and what do I do now? Why would it take 3 weeks later for this to occur. Is there a connection or relay that I can clean out . Need suggestions. Thanks.
C1278 H (temporarily inhibited by pcm). I
assume that the pcm also got wet and what do I do now? Why would it take 3 weeks later for this to occur. Is there a connection or relay that I can clean out . Need suggestions. Thanks.
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
After driving 1 hour on the highway my car's dash message was reduced engine power and service active handling. I could not get the engine to rev over 1 k rpm's. I turned off the car and restarted and then there's no more messages on the dash and the car runs great for 2-3 minutes and then goes back into the reduced engine power mode. Car is 2003 Z06 with p1 procharger installed by andy at A & A in 2005. Car has never had a problem until 3 weeks ago when I got caught in a monsoon rain and I was at a red light when a 18 wheel truck came and created a tidal wave into my car and I put it into gear to try to move and the engine stalled and had to be towed. Water had gotten all the way into the intake manifold and the spark plugs were taken out and water was coming out of the spark plug holes. Everything was dried out and new plugs and wires were placed and the car ran great until today. I cleared the codes and the only 2 codes now are P1515 H C (Command vs Actual throttle perfomance (pcm module)) and
C1278 H (temporarily inhibited by pcm). I assume that the pcm also got wet and what do I do now? Why would it take 3 weeks later for this to occur. Is there a connection or relay that I can clean out . Need suggestions. Thanks.
C1278 H (temporarily inhibited by pcm). I
assume that the pcm also got wet and what do I do now? Why would it take 3 weeks later for this to occur. Is there a connection or relay that I can clean out . Need suggestions. Thanks.
Drifting
Joined: Jan 2008
Posts: 1,722
Likes: 138
From: Florida
St. Jude Donor '09
I would start by verifying that all the grounds are free of corrosion and properly secured and that all the connectors (especially the ones going to the PCM) are free of any moisture and corrosion or debris.
The service manual is invaluable when diagnosing problems like this, do you have one? If not I suggest you do or get an ALLDATA DIY account.
The service manual is invaluable when diagnosing problems like this, do you have one? If not I suggest you do or get an ALLDATA DIY account.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
When the problem happens...... IMMEDIATELY read and write down the DTCs that are displayed in the IPC DIC.
Read them without turning the engine or ignition OFF. If there are a TON of DTCs,,, clear them ALL and read the next error issue and see what returns. POST THOSE DTCs!
The reduced engine power has to do with a throttle by wire issue!
The PCM and TAC module sense an error and default to minimun throttle opening. Enough to get to the side of the road!
READING YOUR Engine Diagnostic Trouble Codes (DTC)
This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.
Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.
If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.
These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs
Here are some very good sites that explain what DTC mean:
http://www.gearchatter.com/viewtopic11755.php
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix when you post your DTCs!!
BC
Read them without turning the engine or ignition OFF. If there are a TON of DTCs,,, clear them ALL and read the next error issue and see what returns. POST THOSE DTCs!
The reduced engine power has to do with a throttle by wire issue!
The PCM and TAC module sense an error and default to minimun throttle opening. Enough to get to the side of the road!
READING YOUR Engine Diagnostic Trouble Codes (DTC)
This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.
Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.
If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.
These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs
Here are some very good sites that explain what DTC mean:
http://www.gearchatter.com/viewtopic11755.php
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix when you post your DTCs!!
BC
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
When the problem happens...... IMMEDIATELY read and write down the DTCs that are displayed in the IPC DIC.
Read them without turning the engine or ignition OFF. If there are a TON of DTCs,,, clear them ALL and read the next error issue and see what returns. POST THOSE DTCs!
The reduced engine power has to do with a throttle by wire issue!
The PCM and TAC module sense an error and default to minimun throttle opening. Enough to get to the side of the road!
READING YOUR Engine Diagnostic Trouble Codes (DTC)
This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.
Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.
If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.
These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs
Here are some very good sites that explain what DTC mean:
http://www.gearchatter.com/viewtopic11755.php
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix when you post your DTCs!!
BC
Read them without turning the engine or ignition OFF. If there are a TON of DTCs,,, clear them ALL and read the next error issue and see what returns. POST THOSE DTCs!
The reduced engine power has to do with a throttle by wire issue!
The PCM and TAC module sense an error and default to minimun throttle opening. Enough to get to the side of the road!
READING YOUR Engine Diagnostic Trouble Codes (DTC)
This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.
Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.
If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
You can read the DTCs while the engine is running. If you turn the engine OFF and then back ON, that can clear some DTCs that may be important with identifying a problem. One example is a Misfire DTC (p-0300) If the engine is shut down, the DTC will clear.
These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs
Here are some very good sites that explain what DTC mean:
http://www.gearchatter.com/viewtopic11755.php
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix when you post your DTCs!!
BC
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
I changed the throttle position sensor and I still get the same 2 codes and the engine initially starts fine but if I rev past 2 K rpm's then it goes into reduced engine mode. I already blew over $1500 at the small town mechanic but I guess I will need to go the dealership. Any other suggestions?
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Thread Starter
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Would an air leak in the intake manifold cause these codes to come on and make the engine go into reduced mode. The mechanic told me that initially there was an air leak when he placed the intake manifold back on after drying everything out and then he told me that the leak went away. Thanks.
Thread Starter
Instructor
Joined: Oct 2010
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Would an air leak in the intake manifold cause these codes to come on and make the engine go into reduced mode. The mechanic told me that initially there was an air leak when he placed the intake manifold back on after drying everything out and then he told me that the leak went away. Thanks.
Melting Slicks
Joined: Jun 2005
Posts: 3,088
Likes: 61
From: NY- 2013 Corvette Challenge Champion-2013 Index Combo Champion 2015 CC/MM Champion
St. Jude Donor '07
P1515 is whats putting you into reduced power mode.Did you have the car tuned recently? Did you wash the car? If not maybe a TP sensor or TAC module could be bad.Check the wires by the TPS and make sure none are broken off.OK I just went back and read your 1st post,If you know how take the PCM out,Take the plugs off the pcm and check for water or corrosion and do the same for the TAC module.Disconnect battery 1st..............Paul
Last edited by DRIVER456; Sep 3, 2011 at 06:37 PM.
Thread Starter
Instructor
Joined: Oct 2010
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P1515 is whats putting you into reduced power mode.Did you have the car tuned recently? Did you wash the car? If not maybe a TP sensor or TAC module could be bad.Check the wires by the TPS and make sure none are broken off.OK I just went back and read your 1st post,If you know how take the PCM out,Take the plugs off the pcm and check for water or corrosion and do the same for the TAC module.Disconnect battery 1st..............Paul
If there is no corrosion and if I want to test if the tac module is the problem, can the TAC module be switched from a 2000
C5 to a 2003 Zo6? Thanks.
Melting Slicks
Joined: Jun 2005
Posts: 3,088
Likes: 61
From: NY- 2013 Corvette Challenge Champion-2013 Index Combo Champion 2015 CC/MM Champion
St. Jude Donor '07
I was planning on taking the front right inner wheel liner off tomorrow and see if there was enough room to get to the pcm and it's connectors. Do you have to take the right front fender off to get to all the screws and connectors or can it all be done by removing the liner?
If there is no corrosion and if I want to test if the tac module is the problem, can the TAC module be switched from a 2000
C5 to a 2003 Zo6? Thanks.
If there is no corrosion and if I want to test if the tac module is the problem, can the TAC module be switched from a 2000
C5 to a 2003 Zo6? Thanks.
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
You don't have to take the whole liner out,Its a smaller piece of the fender well behind the pass. side front tire.Also check your codes again,When it goes into reduced power mode don't clear the codes check them 1st and see if your getting a P1514 code,I read your 1st post again and see you have a SC.............Paul
Zo6. I disconnected, cleaned and sprayed all the connectors to the TAC module and PCM( they were pretty clean) and I still get the reduced engine mode. Before I switch the tac module from my other C5, I want to know if they are interchangeable.
Thanks.
Melting Slicks
Joined: Jun 2005
Posts: 3,088
Likes: 61
From: NY- 2013 Corvette Challenge Champion-2013 Index Combo Champion 2015 CC/MM Champion
St. Jude Donor '07
Not sure on the TAC module.As soon as the car goes into reduced power mode check the codes again.Are the plugs the same on the tac modules?
Thread Starter
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Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Well,,, here are the definitions for each DTC. Reading them and following the trouble procedure for each can help resolve the issue
DTC C-1278 is a result of the P-1515 DTC
Remove the air bridge and turn the ignition ON / engine OFF Clear all the DTCs and have someone press and make SURE that the throttle blade follows the accelerator and moves without any weird noises or binding:
DTC P1515
Circuit. Description
The commanded throttle position, based on accelerator pedal position and possibly on other limiting factors, is compared to the actual throttle position. The 2 values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the commanded and actual throttle position. This DTC sets if the PCM detects an out-of-range condition between the commanded and the actual pedal position.
Conditions for Running the DTC
DTCs P0601, P0602, P0604, P0606, P1516, P1517, or P1518 are not set.
DTCs P1120, P1220 and P1221 are not set at the same time, or DTCs P1120 and P1220 are not set at the same time.
The ignition switch is in the crank or the run position.
The ignition voltage is greater than 8.5 volts.
The TAC system is not in the battery saver mode.
Conditions for Setting the DTC
The PCM detects that the commanded and the actual throttle positions are not within a calibrated range of each other.
All above conditions met for less than 1 second.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
If you do not find any trouble, inspect for mechanical problems or for binding that may be temperature related. Components may not move freely in extreme heat or cold due to the presence of contaminants or due to ice formation.
Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
For an intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
If the throttle position (TP) Indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or with the TP sensor.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
DTC P1515 - Predicted vs. Actual Throttle Position Performance (TAC) Step
Action
Yes
No
Schematic reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Are DTCs P1518 and P1221 both set also?
Go to DTC P1518
Go to Step 3
3
Is DTC P1221 set?
Go to DTC P1221
Go to Step 4
4
Important
The next test must be started within 15 seconds after the ignition is turned ON.
Turn OFF the ignition for 15 seconds.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP sensor 1 and TP sensor 2 angle parameters.
Slowly depress the accelerator pedal to wide open throttle (WOT) and slowly return the pedal to the released position.
Does the scan tool indicate both angle parameters increasing as the pedal is depressed to WOT and decreasing as the pedal is moved to the released position?
Go to Diagnostic Aids
Go to Step 5
5
Turn OFF the ignition.
Remove the air duct from the throttle body assembly.
Disconnect the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF.
With your hand, slowly open the throttle blade to WOT and then to the closed throttle position while observing the TP sensor 1 and TP sensor 2 angle parameters on the scan tool.
Does the scan tool indicate both angle parameters increasing as the throttle plate is moved to WOT and decreasing as the throttle plate is moved to the closed position?
Go to Step 6
Go to Step 13
6
Turn OFF the ignition.
Disconnect the TAC module harness connector containing the throttle actuator control motor circuits.
Turn ON the ignition, with the engine OFF.
With a DMM, test the throttle actuator control motor circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 7
7
With a DMM, test each throttle actuator control motor circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 8
8
With a DMM, test each throttle actuator control motor circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 9
9
Disconnect the other TAC module harness connector.
With a DMM, test for a short between each throttle actuator control motor circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 10
10
Turn OFF the ignition.
Reconnect the TAC module.
Connect a test lamp between the two throttle actuator control motor terminals at the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF and observe the test lamp.
Did the test lamp illuminate briefly when the ignition was turned ON?
Go to Step 11
Go to Step 13
11
Inspect for poor connections at the throttle actuator control motor harness connector. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 12
12
Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?
Go to Step 15
--
13
Inspect for poor connections at the TAC module harness connectors. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 14
14
Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement .
Did you complete the replacement?
Go to Step 15
--
15
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running as specified in the supporting text.
Does the DTC run and pass?
Go to Step 16
Go to Step 2
16
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK
--------------------------------------------------------------------------------
Document ID# 706705
2002 Chevrolet Corvette
DTC C1278
Circuit Description
The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.
The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.
The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.
When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The PCM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The PCM will typically set a DTC and the EBCM will set this DTC.
Action Taken When the DTC Sets
If equipped, the following actions occur:
The EBCM disables the TCS/VSES for the duration of the ignition cycle.
The Traction Control and Active Handling indicator turns ON.
The DIC displays the following messages:
Service Traction System
Service Active Handling
The ABS remains functional.
Conditions for Clearing the DTC
The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
Diagnostic Aids
This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system.
Step
Action
Yes
No
Schematic Reference: ABS Schematics
1
Did you perform the ABS Diagnostic System Check?
Go to Diagnostic System Check - Engine Controls in Engine Controls - 5.7L
Go to Diagnostic System Check - ABS
--------------------------------------------------------------------------------
Document ID# 670695
2002 Chevrolet Corvette
DTC C-1278 is a result of the P-1515 DTC
Remove the air bridge and turn the ignition ON / engine OFF Clear all the DTCs and have someone press and make SURE that the throttle blade follows the accelerator and moves without any weird noises or binding:
DTC P1515
Circuit. Description
The commanded throttle position, based on accelerator pedal position and possibly on other limiting factors, is compared to the actual throttle position. The 2 values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the commanded and actual throttle position. This DTC sets if the PCM detects an out-of-range condition between the commanded and the actual pedal position.
Conditions for Running the DTC
DTCs P0601, P0602, P0604, P0606, P1516, P1517, or P1518 are not set.
DTCs P1120, P1220 and P1221 are not set at the same time, or DTCs P1120 and P1220 are not set at the same time.
The ignition switch is in the crank or the run position.
The ignition voltage is greater than 8.5 volts.
The TAC system is not in the battery saver mode.
Conditions for Setting the DTC
The PCM detects that the commanded and the actual throttle positions are not within a calibrated range of each other.
All above conditions met for less than 1 second.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
If you do not find any trouble, inspect for mechanical problems or for binding that may be temperature related. Components may not move freely in extreme heat or cold due to the presence of contaminants or due to ice formation.
Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
For an intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
If the throttle position (TP) Indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or with the TP sensor.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
DTC P1515 - Predicted vs. Actual Throttle Position Performance (TAC) Step
Action
Yes
No
Schematic reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Are DTCs P1518 and P1221 both set also?
Go to DTC P1518
Go to Step 3
3
Is DTC P1221 set?
Go to DTC P1221
Go to Step 4
4
Important
The next test must be started within 15 seconds after the ignition is turned ON.
Turn OFF the ignition for 15 seconds.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP sensor 1 and TP sensor 2 angle parameters.
Slowly depress the accelerator pedal to wide open throttle (WOT) and slowly return the pedal to the released position.
Does the scan tool indicate both angle parameters increasing as the pedal is depressed to WOT and decreasing as the pedal is moved to the released position?
Go to Diagnostic Aids
Go to Step 5
5
Turn OFF the ignition.
Remove the air duct from the throttle body assembly.
Disconnect the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF.
With your hand, slowly open the throttle blade to WOT and then to the closed throttle position while observing the TP sensor 1 and TP sensor 2 angle parameters on the scan tool.
Does the scan tool indicate both angle parameters increasing as the throttle plate is moved to WOT and decreasing as the throttle plate is moved to the closed position?
Go to Step 6
Go to Step 13
6
Turn OFF the ignition.
Disconnect the TAC module harness connector containing the throttle actuator control motor circuits.
Turn ON the ignition, with the engine OFF.
With a DMM, test the throttle actuator control motor circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 7
7
With a DMM, test each throttle actuator control motor circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 8
8
With a DMM, test each throttle actuator control motor circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 9
9
Disconnect the other TAC module harness connector.
With a DMM, test for a short between each throttle actuator control motor circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 10
10
Turn OFF the ignition.
Reconnect the TAC module.
Connect a test lamp between the two throttle actuator control motor terminals at the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF and observe the test lamp.
Did the test lamp illuminate briefly when the ignition was turned ON?
Go to Step 11
Go to Step 13
11
Inspect for poor connections at the throttle actuator control motor harness connector. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 12
12
Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?
Go to Step 15
--
13
Inspect for poor connections at the TAC module harness connectors. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 14
14
Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement .
Did you complete the replacement?
Go to Step 15
--
15
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running as specified in the supporting text.
Does the DTC run and pass?
Go to Step 16
Go to Step 2
16
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK
--------------------------------------------------------------------------------
Document ID# 706705
2002 Chevrolet Corvette
DTC C1278
Circuit Description
The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.
The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.
The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.
When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The PCM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The PCM will typically set a DTC and the EBCM will set this DTC.
Action Taken When the DTC Sets
If equipped, the following actions occur:
The EBCM disables the TCS/VSES for the duration of the ignition cycle.
The Traction Control and Active Handling indicator turns ON.
The DIC displays the following messages:
Service Traction System
Service Active Handling
The ABS remains functional.
Conditions for Clearing the DTC
The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
Diagnostic Aids
This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system.
Step
Action
Yes
No
Schematic Reference: ABS Schematics
1
Did you perform the ABS Diagnostic System Check?
Go to Diagnostic System Check - Engine Controls in Engine Controls - 5.7L
Go to Diagnostic System Check - ABS
--------------------------------------------------------------------------------
Document ID# 670695
2002 Chevrolet Corvette
Thread Starter
Instructor
Joined: Oct 2010
Posts: 140
Likes: 0
Well,,, here are the definitions for each DTC. Reading them and following the trouble procedure for each can help resolve the issue
DTC C-1278 is a result of the P-1515 DTC
Remove the air bridge and turn the ignition ON / engine OFF Clear all the DTCs and have someone press and make SURE that the throttle blade follows the accelerator and moves without any weird noises or binding:
DTC P1515
Circuit. Description
The commanded throttle position, based on accelerator pedal position and possibly on other limiting factors, is compared to the actual throttle position. The 2 values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the commanded and actual throttle position. This DTC sets if the PCM detects an out-of-range condition between the commanded and the actual pedal position.
Conditions for Running the DTC
DTCs P0601, P0602, P0604, P0606, P1516, P1517, or P1518 are not set.
DTCs P1120, P1220 and P1221 are not set at the same time, or DTCs P1120 and P1220 are not set at the same time.
The ignition switch is in the crank or the run position.
The ignition voltage is greater than 8.5 volts.
The TAC system is not in the battery saver mode.
Conditions for Setting the DTC
The PCM detects that the commanded and the actual throttle positions are not within a calibrated range of each other.
All above conditions met for less than 1 second.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
If you do not find any trouble, inspect for mechanical problems or for binding that may be temperature related. Components may not move freely in extreme heat or cold due to the presence of contaminants or due to ice formation.
Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
For an intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
If the throttle position (TP) Indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or with the TP sensor.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
DTC P1515 - Predicted vs. Actual Throttle Position Performance (TAC) Step
Action
Yes
No
Schematic reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Are DTCs P1518 and P1221 both set also?
Go to DTC P1518
Go to Step 3
3
Is DTC P1221 set?
Go to DTC P1221
Go to Step 4
4
Important
The next test must be started within 15 seconds after the ignition is turned ON.
Turn OFF the ignition for 15 seconds.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP sensor 1 and TP sensor 2 angle parameters.
Slowly depress the accelerator pedal to wide open throttle (WOT) and slowly return the pedal to the released position.
Does the scan tool indicate both angle parameters increasing as the pedal is depressed to WOT and decreasing as the pedal is moved to the released position?
Go to Diagnostic Aids
Go to Step 5
5
Turn OFF the ignition.
Remove the air duct from the throttle body assembly.
Disconnect the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF.
With your hand, slowly open the throttle blade to WOT and then to the closed throttle position while observing the TP sensor 1 and TP sensor 2 angle parameters on the scan tool.
Does the scan tool indicate both angle parameters increasing as the throttle plate is moved to WOT and decreasing as the throttle plate is moved to the closed position?
Go to Step 6
Go to Step 13
6
Turn OFF the ignition.
Disconnect the TAC module harness connector containing the throttle actuator control motor circuits.
Turn ON the ignition, with the engine OFF.
With a DMM, test the throttle actuator control motor circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 7
7
With a DMM, test each throttle actuator control motor circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 8
8
With a DMM, test each throttle actuator control motor circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 9
9
Disconnect the other TAC module harness connector.
With a DMM, test for a short between each throttle actuator control motor circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 10
10
Turn OFF the ignition.
Reconnect the TAC module.
Connect a test lamp between the two throttle actuator control motor terminals at the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF and observe the test lamp.
Did the test lamp illuminate briefly when the ignition was turned ON?
Go to Step 11
Go to Step 13
11
Inspect for poor connections at the throttle actuator control motor harness connector. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 12
12
Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?
Go to Step 15
--
13
Inspect for poor connections at the TAC module harness connectors. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 14
14
Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement .
Did you complete the replacement?
Go to Step 15
--
15
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running as specified in the supporting text.
Does the DTC run and pass?
Go to Step 16
Go to Step 2
16
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK
--------------------------------------------------------------------------------
Document ID# 706705
2002 Chevrolet Corvette
DTC C1278
Circuit Description
The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.
The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.
The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.
When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The PCM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The PCM will typically set a DTC and the EBCM will set this DTC.
Action Taken When the DTC Sets
If equipped, the following actions occur:
The EBCM disables the TCS/VSES for the duration of the ignition cycle.
The Traction Control and Active Handling indicator turns ON.
The DIC displays the following messages:
Service Traction System
Service Active Handling
The ABS remains functional.
Conditions for Clearing the DTC
The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
Diagnostic Aids
This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system.
Step
Action
Yes
No
Schematic Reference: ABS Schematics
1
Did you perform the ABS Diagnostic System Check?
Go to Diagnostic System Check - Engine Controls in Engine Controls - 5.7L
Go to Diagnostic System Check - ABS
--------------------------------------------------------------------------------
Document ID# 670695
2002 Chevrolet Corvette
DTC C-1278 is a result of the P-1515 DTC
Remove the air bridge and turn the ignition ON / engine OFF Clear all the DTCs and have someone press and make SURE that the throttle blade follows the accelerator and moves without any weird noises or binding:
DTC P1515
Circuit. Description
The commanded throttle position, based on accelerator pedal position and possibly on other limiting factors, is compared to the actual throttle position. The 2 values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the commanded and actual throttle position. This DTC sets if the PCM detects an out-of-range condition between the commanded and the actual pedal position.
Conditions for Running the DTC
DTCs P0601, P0602, P0604, P0606, P1516, P1517, or P1518 are not set.
DTCs P1120, P1220 and P1221 are not set at the same time, or DTCs P1120 and P1220 are not set at the same time.
The ignition switch is in the crank or the run position.
The ignition voltage is greater than 8.5 volts.
The TAC system is not in the battery saver mode.
Conditions for Setting the DTC
The PCM detects that the commanded and the actual throttle positions are not within a calibrated range of each other.
All above conditions met for less than 1 second.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
If you do not find any trouble, inspect for mechanical problems or for binding that may be temperature related. Components may not move freely in extreme heat or cold due to the presence of contaminants or due to ice formation.
Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
For an intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
If the throttle position (TP) Indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or with the TP sensor.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
DTC P1515 - Predicted vs. Actual Throttle Position Performance (TAC) Step
Action
Yes
No
Schematic reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Are DTCs P1518 and P1221 both set also?
Go to DTC P1518
Go to Step 3
3
Is DTC P1221 set?
Go to DTC P1221
Go to Step 4
4
Important
The next test must be started within 15 seconds after the ignition is turned ON.
Turn OFF the ignition for 15 seconds.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the TP sensor 1 and TP sensor 2 angle parameters.
Slowly depress the accelerator pedal to wide open throttle (WOT) and slowly return the pedal to the released position.
Does the scan tool indicate both angle parameters increasing as the pedal is depressed to WOT and decreasing as the pedal is moved to the released position?
Go to Diagnostic Aids
Go to Step 5
5
Turn OFF the ignition.
Remove the air duct from the throttle body assembly.
Disconnect the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF.
With your hand, slowly open the throttle blade to WOT and then to the closed throttle position while observing the TP sensor 1 and TP sensor 2 angle parameters on the scan tool.
Does the scan tool indicate both angle parameters increasing as the throttle plate is moved to WOT and decreasing as the throttle plate is moved to the closed position?
Go to Step 6
Go to Step 13
6
Turn OFF the ignition.
Disconnect the TAC module harness connector containing the throttle actuator control motor circuits.
Turn ON the ignition, with the engine OFF.
With a DMM, test the throttle actuator control motor circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 7
7
With a DMM, test each throttle actuator control motor circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 8
8
With a DMM, test each throttle actuator control motor circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 9
9
Disconnect the other TAC module harness connector.
With a DMM, test for a short between each throttle actuator control motor circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 10
10
Turn OFF the ignition.
Reconnect the TAC module.
Connect a test lamp between the two throttle actuator control motor terminals at the throttle actuator control motor harness connector.
Turn ON the ignition, with the engine OFF and observe the test lamp.
Did the test lamp illuminate briefly when the ignition was turned ON?
Go to Step 11
Go to Step 13
11
Inspect for poor connections at the throttle actuator control motor harness connector. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 12
12
Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .
Did you complete the replacement?
Go to Step 15
--
13
Inspect for poor connections at the TAC module harness connectors. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
Go to Step 15
Go to Step 14
14
Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement .
Did you complete the replacement?
Go to Step 15
--
15
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running as specified in the supporting text.
Does the DTC run and pass?
Go to Step 16
Go to Step 2
16
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK
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Document ID# 706705
2002 Chevrolet Corvette
DTC C1278
Circuit Description
The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.
The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.
The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.
When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The PCM diagnoses a condition preventing the engine control portion of the traction control function and sends a serial data message to the EBCM indicating that torque reduction is not allowed. The PCM will typically set a DTC and the EBCM will set this DTC.
Action Taken When the DTC Sets
If equipped, the following actions occur:
The EBCM disables the TCS/VSES for the duration of the ignition cycle.
The Traction Control and Active Handling indicator turns ON.
The DIC displays the following messages:
Service Traction System
Service Active Handling
The ABS remains functional.
Conditions for Clearing the DTC
The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
Diagnostic Aids
This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system.
Step
Action
Yes
No
Schematic Reference: ABS Schematics
1
Did you perform the ABS Diagnostic System Check?
Go to Diagnostic System Check - Engine Controls in Engine Controls - 5.7L
Go to Diagnostic System Check - ABS
--------------------------------------------------------------------------------
Document ID# 670695
2002 Chevrolet Corvette
