P1518 reduced eng. power
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 768
Likes: 27
From: Whittier CA
P1518 reduced eng. power
Hey guys need some ideas. reduced eng. power shows and now no start. After a long drive thru high winds and blowing sand she was runing fine, stoped for gas then reduced eng. power showed up and cranked but would not start. After some tries she fired up and ran fine but check eng. on. Drove home ran good and strong. Tried when I got home and she started right up. Came out this am no start. Went thru codes found p1518 cleared and started. Shut it off and no restart. Clear code and it pops right back up in about 2sec. Can not restart. Am I looking at a new Throttle actuator control. (TAC)?
Sorry it is a C5 ZO6 2003
Sorry it is a C5 ZO6 2003
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
How are you reading the DTCs??? Are you using the DIC Internal Code reader?
There are several things that can cause this. Do you have any engine modifications?
Make SURE that you post any other DTCs that may be reporting and if they are a C or H
READING YOUR C5 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!!
NOTE!!! Start the car and let it idle. Then take it for a drive and cause the problem to occur. When you return home pull the codes BEFORE you shut off the engine.
Do NOT discount the codes with the H following them. They can provide an audit trail for issues going on with the car. They ARE important in diagnosing problems.
Post ALL the codes that you pull with the engine running..........
Some codes go away WITHOUT setting an H code when you shut the engine off. I suspect you will have several codes that will show C or HC that do NOT show when the engine is turned off.
There are several things that can cause this. Do you have any engine modifications?
Make SURE that you post any other DTCs that may be reporting and if they are a C or H
READING YOUR C5 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!!
NOTE!!! Start the car and let it idle. Then take it for a drive and cause the problem to occur. When you return home pull the codes BEFORE you shut off the engine.
Do NOT discount the codes with the H following them. They can provide an audit trail for issues going on with the car. They ARE important in diagnosing problems.
Post ALL the codes that you pull with the engine running..........
Some codes go away WITHOUT setting an H code when you shut the engine off. I suspect you will have several codes that will show C or HC that do NOT show when the engine is turned off.
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 768
Likes: 27
From: Whittier CA
Thanks Bill I read the code with the in.dash unit. I have both C and H the only other code I had was for the HVAC witch I get from time to time. the car has a tune in it that was done a year ago. the only mod. I have is the air intake that was done 2years ago. I can not get it to start now.
Last edited by vinceg; Apr 9, 2013 at 04:17 PM.
Melting Slicks
Joined: Nov 1999
Posts: 2,347
Likes: 857
From: MI
Cruise-In VI Veteran
For a 2003 Model year Vette
DTC P1518
Circuit Description
The throttle actuator control (TAC) module and the powertrain control module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity, but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.
Conditions for Running the DTC
• The ignition switch is in the crank or the run position.
• The ignition voltage is greater than 5.23 volts.
Conditions for Setting the DTC
• Invalid or missing serial data messages are detected for a predetermined amount of time.
• All of the 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
• DTC P1518 sets if the battery voltage is low. If the customer's concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs that may have set from the low battery voltage condition from the memory.
• DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness, such as the cruise, or the brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.
• DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned off. When the ignition switch is turned on, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.
• Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.
• Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no DTC circuit or component conditions found during diagnostic testing.
• When the TAC module detects a problem 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 problem may correct more than 1 DTC. Keep this in mind when reviewing captured DTC info.
• For an intermittent condition, refer to Intermittent Conditions .
THROT CONT Fuse Underhood Electrical Center Terminal Identification
Front of Vehicle
Left Side of Vehicle
Ignition Voltage
TAC Module
Right Side of Vehicle
Test Description
The numbers below refer to the step numbers on the diagnostic table.
This step determines if the IGN relay is suppling a voltage to the THROT CONT fuse.
Increasing the engine speed to 3,000 RPM aids in locating a shorted throttle actuator motor control circuit. Depending on the polarity of the throttle actuator motor transistors, this DTC may not set with a fault in the control circuits. The throttle actuator motor is a bi-directional DC motor. Raising the engine speed changes the polarity of the transistors in the throttle actuator motor. This occurs because 1 set of the transistors is near 0 volts, and the other set is at high B+. Therefore, if 1 set of transistors is at a low voltage and the corresponding circuit is shorted low, DTC P1518 will not set. When the polarity of the transistors change this DTC sets. If this DTC does not Fail This Ignition, continue to monitor this DTC status while moving related harnesses and connectors.
When the TAC module detects a condition within the TAC system, more than 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 the components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
Step
Action
Values
Yes
No
Schematic Reference: Engine Controls Schematics
Connector End View References: Powertrain Control Module Connector End Views , Electronic Throttle Actuator Control Module Connector End Views , or Engine Controls Connector End Views
1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Turn ON the ignition, with the engine OFF.
Remove the cover from the underhood electrical center.
With a test lamp connected to ground, test both sides of the THROT CONT fuse.
Does the test lamp illuminate on at least 1 side of the fuse?
--
Go to Step 3
Go to Ignition Relay Diagnosis
3
Turn OFF the ignition.
With a test lamp connected to ground, test for voltage at the THROT CONT fuse.
Does the test lamp illuminate?
--
Go to Step 22
Go to Step 4
4
Install a scan tool.
Is DTC P0606 also set?
--
Go to DTC P0601, P0602, P0603, P0604, P0605, P0606, P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610
Go to Step 5
5
Important: If the Driver Information Center is displaying Reduced Engine Power, go to Step 6.
Start the engine.
Increase the engine speed to 3,000 RPM, if possible.
Monitor the diagnostic trouble code (DTC) Info option using the scan tool.
Does the scan tool indicate this DTC failed this ignition?
--
Go to Step 6
Go to Diagnostic Aids
6
Turn OFF the ignition.
Disconnect the throttle actuator motor harness connector.
Turn ON the ignition, with the engine OFF.
With a DMM, test for voltage at both throttle actuator motor control circuits.
Does the DMM indicate voltage on both circuits above the specified value?
8 V
Go to Step 12
Go to Step 7
7
Turn OFF the ignition.
With a DMM, test both throttle actuator motor control circuits for continuity to ground.
Does the DMM indicate continuity to ground?
--
Go to Step 10
Go to Step 8
8
Turn OFF the ignition.
Remove the THROT CONT fuse.
With a DMM, test the TAC side of the fuse terminal for continuity to ground. Refer to Diagnostic Aids for terminal identification table.
Does the DMM indicate continuity to ground?
--
Go to Step 9
Go to Step 11
9
Disconnect the TAC module 16-way harness connector.
With a DMM, test the TAC side of the fuse terminal 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 28
Go to Step 24
10
Disconnect the TAC module 16-way harness connector.
With a DMM, test the throttle actuator motor control circuits for a short to ground at the TAC module 16-way harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 24
11
Turn OFF the ignition.
Disconnect the TAC module 16-way harness connector.
With a DMM, test the TAC module ignition feed 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 28
Go to Step 24
12
Turn OFF the ignition.
Disconnect the TAC module 16-way connector.
Turn ON the ignition, with the engine OFF
With a DMM, test for a short to voltage at both Throttle Actuator Motor control circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 13
13
Turn OFF the ignition.
Disconnect the TAC module 10-way harness connector.
With a DMM, Test for a short between each throttle actuator motor control 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 28
Go to Step 14
14
With a DMM, test for an open or for high resistance in the TAC module ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 15
15
With a DMM, test for voltage on the serial data circuits at the TAC module 16-way harness connector.
Does the DMM indicate voltage within the specified values for both circuits?
0-4.5 V
Go to Step 16
Go to Step 18
16
Turn OFF the ignition.
With a DMM, test both serial data circuits at the TAC module 16-way harness connector for continuity to ground.
Does the DMM indicate OL for both circuits?
--
Go to Step 20
Go to Step 17
17
Disconnect the PCM connector containing the TAC module serial data circuits.
With a DMM, test both serial data circuits at the TAC module 16-way connector 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 28
Go to Step 18
18
With a DMM, test for a short between both serial data circuits and all other circuits at the PCM and TAC module harness connectors. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 19
19
With a DMM, test for a short to voltage on both serial data circuits at the TAC module 16-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 25
20
Disconnect the PCM connector that contains the TAC module serial data circuits.
With a DMM, test each serial data circuit between the TAC module 16-way harness connector and the PCM harness connector 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 28
Go to Step 21
21
Reconnect the PCM.
Turn ON the ignition.
With a DMM, test for voltage on the serial data circuit at the TAC module 16-way harness connector.
Does the DMM indicate voltage at the specified value?
0 V
Go to Step 25
Go to Step 24
22
Turn OFF the ignition.
Disconnect the 16-way TAC module harness connector.
Test the TAC module ignition feed circuit for a short to battery voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 23
23
Turn ON the ignition.
Test both 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 28
Go to Step 24
24
Test for poor connections at the TAC module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 26
25
Test for poor connections at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 27
26
Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .
Did you complete the replacement?
--
Go to Step 28
--
27
Replace the PCM. Refer to Powertrain Control Module Replacement .
Did you complete the replacement?
--
Go to Step 28
--
28
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 the DTC as specified in the supporting text.
Does the DTC run and pass?
--
Go to Step 29
Go to Step 2
29
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
DTC P1518
Circuit Description
The throttle actuator control (TAC) module and the powertrain control module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity, but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.
Conditions for Running the DTC
• The ignition switch is in the crank or the run position.
• The ignition voltage is greater than 5.23 volts.
Conditions for Setting the DTC
• Invalid or missing serial data messages are detected for a predetermined amount of time.
• All of the 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
• DTC P1518 sets if the battery voltage is low. If the customer's concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs that may have set from the low battery voltage condition from the memory.
• DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness, such as the cruise, or the brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.
• DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned off. When the ignition switch is turned on, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.
• Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.
• Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no DTC circuit or component conditions found during diagnostic testing.
• When the TAC module detects a problem 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 problem may correct more than 1 DTC. Keep this in mind when reviewing captured DTC info.
• For an intermittent condition, refer to Intermittent Conditions .
THROT CONT Fuse Underhood Electrical Center Terminal Identification
Front of Vehicle
Left Side of Vehicle
Ignition Voltage
TAC Module
Right Side of Vehicle
Test Description
The numbers below refer to the step numbers on the diagnostic table.
This step determines if the IGN relay is suppling a voltage to the THROT CONT fuse.
Increasing the engine speed to 3,000 RPM aids in locating a shorted throttle actuator motor control circuit. Depending on the polarity of the throttle actuator motor transistors, this DTC may not set with a fault in the control circuits. The throttle actuator motor is a bi-directional DC motor. Raising the engine speed changes the polarity of the transistors in the throttle actuator motor. This occurs because 1 set of the transistors is near 0 volts, and the other set is at high B+. Therefore, if 1 set of transistors is at a low voltage and the corresponding circuit is shorted low, DTC P1518 will not set. When the polarity of the transistors change this DTC sets. If this DTC does not Fail This Ignition, continue to monitor this DTC status while moving related harnesses and connectors.
When the TAC module detects a condition within the TAC system, more than 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 the components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
Step
Action
Values
Yes
No
Schematic Reference: Engine Controls Schematics
Connector End View References: Powertrain Control Module Connector End Views , Electronic Throttle Actuator Control Module Connector End Views , or Engine Controls Connector End Views
1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Turn ON the ignition, with the engine OFF.
Remove the cover from the underhood electrical center.
With a test lamp connected to ground, test both sides of the THROT CONT fuse.
Does the test lamp illuminate on at least 1 side of the fuse?
--
Go to Step 3
Go to Ignition Relay Diagnosis
3
Turn OFF the ignition.
With a test lamp connected to ground, test for voltage at the THROT CONT fuse.
Does the test lamp illuminate?
--
Go to Step 22
Go to Step 4
4
Install a scan tool.
Is DTC P0606 also set?
--
Go to DTC P0601, P0602, P0603, P0604, P0605, P0606, P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610
Go to Step 5
5
Important: If the Driver Information Center is displaying Reduced Engine Power, go to Step 6.
Start the engine.
Increase the engine speed to 3,000 RPM, if possible.
Monitor the diagnostic trouble code (DTC) Info option using the scan tool.
Does the scan tool indicate this DTC failed this ignition?
--
Go to Step 6
Go to Diagnostic Aids
6
Turn OFF the ignition.
Disconnect the throttle actuator motor harness connector.
Turn ON the ignition, with the engine OFF.
With a DMM, test for voltage at both throttle actuator motor control circuits.
Does the DMM indicate voltage on both circuits above the specified value?
8 V
Go to Step 12
Go to Step 7
7
Turn OFF the ignition.
With a DMM, test both throttle actuator motor control circuits for continuity to ground.
Does the DMM indicate continuity to ground?
--
Go to Step 10
Go to Step 8
8
Turn OFF the ignition.
Remove the THROT CONT fuse.
With a DMM, test the TAC side of the fuse terminal for continuity to ground. Refer to Diagnostic Aids for terminal identification table.
Does the DMM indicate continuity to ground?
--
Go to Step 9
Go to Step 11
9
Disconnect the TAC module 16-way harness connector.
With a DMM, test the TAC side of the fuse terminal 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 28
Go to Step 24
10
Disconnect the TAC module 16-way harness connector.
With a DMM, test the throttle actuator motor control circuits for a short to ground at the TAC module 16-way harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 24
11
Turn OFF the ignition.
Disconnect the TAC module 16-way harness connector.
With a DMM, test the TAC module ignition feed 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 28
Go to Step 24
12
Turn OFF the ignition.
Disconnect the TAC module 16-way connector.
Turn ON the ignition, with the engine OFF
With a DMM, test for a short to voltage at both Throttle Actuator Motor control circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 13
13
Turn OFF the ignition.
Disconnect the TAC module 10-way harness connector.
With a DMM, Test for a short between each throttle actuator motor control 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 28
Go to Step 14
14
With a DMM, test for an open or for high resistance in the TAC module ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 15
15
With a DMM, test for voltage on the serial data circuits at the TAC module 16-way harness connector.
Does the DMM indicate voltage within the specified values for both circuits?
0-4.5 V
Go to Step 16
Go to Step 18
16
Turn OFF the ignition.
With a DMM, test both serial data circuits at the TAC module 16-way harness connector for continuity to ground.
Does the DMM indicate OL for both circuits?
--
Go to Step 20
Go to Step 17
17
Disconnect the PCM connector containing the TAC module serial data circuits.
With a DMM, test both serial data circuits at the TAC module 16-way connector 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 28
Go to Step 18
18
With a DMM, test for a short between both serial data circuits and all other circuits at the PCM and TAC module harness connectors. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 19
19
With a DMM, test for a short to voltage on both serial data circuits at the TAC module 16-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 25
20
Disconnect the PCM connector that contains the TAC module serial data circuits.
With a DMM, test each serial data circuit between the TAC module 16-way harness connector and the PCM harness connector 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 28
Go to Step 21
21
Reconnect the PCM.
Turn ON the ignition.
With a DMM, test for voltage on the serial data circuit at the TAC module 16-way harness connector.
Does the DMM indicate voltage at the specified value?
0 V
Go to Step 25
Go to Step 24
22
Turn OFF the ignition.
Disconnect the 16-way TAC module harness connector.
Test the TAC module ignition feed circuit for a short to battery voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 23
23
Turn ON the ignition.
Test both 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 28
Go to Step 24
24
Test for poor connections at the TAC module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 26
25
Test for poor connections at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 28
Go to Step 27
26
Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .
Did you complete the replacement?
--
Go to Step 28
--
27
Replace the PCM. Refer to Powertrain Control Module Replacement .
Did you complete the replacement?
--
Go to Step 28
--
28
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 the DTC as specified in the supporting text.
Does the DTC run and pass?
--
Go to Step 29
Go to Step 2
29
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
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 768
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From: Whittier CA
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