help please! "reduced engine power"
Thread Starter
Intermediate
Joined: Aug 2011
Posts: 25
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help please! "reduced engine power"
i just got a 98 c5. started ight up the two times i was looking at it. Now i bring it home and the two mornings i try to start it. "reduced engine power" no start. obd II port no communication. Checked grounds on the first day disconnected battery. Fired right up. Now today nothing worked any ideas gentlemen. im guessing wiring problems. hence the extra ECU in the trunk.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Sound like the guy knew to get you out of the driveway before the 3rd start
1st most engine codes aren't triggered on the 1st sign of a problem--In the ECM there are options for lightiing up a DTC--- They are like "not reported" "Non emissions" "1 trip emiisions" and "2 trips emiisions" Whatever is causing your DTC is set to "2 trips" as the DTC pops up on the 3rd start---
ALSO If you are getting a "NO COMMUNICATION"on your code reader or tuner--GM hides the fuse to the 0DBII port on the CIGARETTE LIGHTER circuit-- all the accerories we use on the cig lighter fries the fuse--but most people don't know how important that fuse is to the ECM
As far as getting it to start and run---You need to get all the codes posted 1st--and we'll go from there--Some codes put the ECM into a limp mode or reduced power mode
If he swapped out to another ECM it will start and die immediately becuase the theft (VATS) system cuts off the fuel--That can be programmed out with a tune--EFILIVE or HP-
1st most engine codes aren't triggered on the 1st sign of a problem--In the ECM there are options for lightiing up a DTC--- They are like "not reported" "Non emissions" "1 trip emiisions" and "2 trips emiisions" Whatever is causing your DTC is set to "2 trips" as the DTC pops up on the 3rd start---
ALSO If you are getting a "NO COMMUNICATION"on your code reader or tuner--GM hides the fuse to the 0DBII port on the CIGARETTE LIGHTER circuit-- all the accerories we use on the cig lighter fries the fuse--but most people don't know how important that fuse is to the ECM
As far as getting it to start and run---You need to get all the codes posted 1st--and we'll go from there--Some codes put the ECM into a limp mode or reduced power mode
If he swapped out to another ECM it will start and die immediately becuase the theft (VATS) system cuts off the fuel--That can be programmed out with a tune--EFILIVE or HP-
Thread Starter
Intermediate
Joined: Aug 2011
Posts: 25
Likes: 0
cleaned up grounds junction behind left headlamp. wiggled some wires on ECU. disconnected battery and she fired up. went to oreillys got some dielectric cleaner and hit the grounds. Read codes with their scanner. EGR code (egr delete), and O2 sensor code due to borla catback and o2 simulaters. We will see tomorrow morning. appreciate the info blu.
Last edited by c5roughneck; Aug 10, 2011 at 01:58 PM.
Tech Contributor
Joined: Aug 2008
Posts: 2,902
Likes: 21
From: Oak Hill Virginia
Courtesy of Bill Curlee
POST DTCS!!!
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.
NOTE and a WARNING. You can read the DTCs while the engine is running. I pull mine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving and cause an accident!!!!! Use common sense and drive safe.
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!!
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.
NOTE and a WARNING. You can read the DTCs while the engine is running. I pull mine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving and cause an accident!!!!! Use common sense and drive safe.
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!!
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
cleaned up grounds junction behind left headlamp. wiggled some wires on ECU. disconnected battery and she fired up. went to oreillys got some dielectric cleaner and hit the grounds. Read codes with their scanner. EGR code (egr delete), and O2 sensor code due to borla catback and o2 simulaters. We will see tomorrow morning. appreciate the info blu.
FIRST THINGS FIRST!! YOU DONT NEED NO STINKING CODE READER!
You can read your OWN codes using the IPC and the DIC:
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!!
SECOND THING... Electrical connections should not be coated in DIELECTRIC GREASE. If you dont want them to corrode, use a anticorrosion compound. Most electrical places selles it and so do marine /boat stores.
The next time that you have an issue,, read the DTC "BEFORE" you turn the ignition OFF!
C5's do not have an EGR Valve.
BC
Thread Starter
Intermediate
Joined: Aug 2011
Posts: 25
Likes: 0
thnx didnt know that about reading codes.
i didnt put dielectric grease i just cleaned the connections with electrical spray. The Egr thing it looks like it had one on the exhaust manifold but plugged up now. i was guessing it was an EGR.
pulled the codes on PCM
0102 C
1445 HC
1571sdm, HC
1518 HC
as well as TCS,SDM,RDCM. NO COMM
thnx for the help gentlemen.
awesome info for a NOOB!!
i didnt put dielectric grease i just cleaned the connections with electrical spray. The Egr thing it looks like it had one on the exhaust manifold but plugged up now. i was guessing it was an EGR.
pulled the codes on PCM
0102 C
1445 HC
1571sdm, HC
1518 HC
as well as TCS,SDM,RDCM. NO COMM
thnx for the help gentlemen.
awesome info for a NOOB!!
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,, seeing that you have a bunch of NO COMMS and one of them is the RDCM...... Open BOTH doors. Grab the rubber tube between the door and door frame and feel for the harness inside the tube with your fingers. Grab the harness and shake the tube& harness hard. See if the codes can be cleared.
BC
BC
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Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
C5's don't have an EGR--so all the EGR codes should be tuned out on the stock factory ECM---Sounds like someone installed a LS1 or LS6 intake out of a Camaro onto your engine--hence the plugged off EGR port--But if you still have the stock ECM you should not be getting any EGR codes regaurdless--
Intermediate
Joined: Aug 2011
Posts: 27
Likes: 3
I just went thru electric hell. The battery leaks onto the wires under it and even though they looked ok they were bad and giving intermittent codes. Mine had to do with the accel pedal giving me reduced engine all the time. If your battery ever leaked I would have the wires check and/or replaced.
Last edited by rolexfix; Aug 12, 2011 at 10:33 PM. Reason: sp
Le Mans Master
Joined: Nov 2005
Posts: 6,993
Likes: 25
