Help Please! PCM/BCM codes only on hot starts...
Thread Starter
Pro
Joined: Nov 2003
Posts: 513
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From: Hotlanta GA
Help Please! PCM/BCM codes only on hot starts...
I've started having a very weird problem where the car will start up and run fine when it's cold but will throw several codes if I stop somewhere and try to start it again. I'm getting tps position errors and tcs disabled messages. (I'm also getting random alternator ltrim errors at highway speeds, but am not sure that's related.)
History: I cleaned all the engine bay grounds a long time ago and just rechecked them while replacing the battery this weekend. (The optima I had in there was 2-3 years old and was getting soft.)
A couple of months ago, I discovered the ls2 tb adapter harness had been worn through by a pulley to the point that a couple of wires were exposed. I cut, soldered and shrinkwrapped those, but now that I'm getting P1120 on hot starts, I'm wondering if the sensor got damaged somehow?
I have not cleaned any of the pcm connections or grounds other than the engine bay. Heck, I've even done the big three upgrade even with the stock radio hoping that would clear up the alternator code.
I'd sure appreciate any pointers....
Thanks,
Dan
History: I cleaned all the engine bay grounds a long time ago and just rechecked them while replacing the battery this weekend. (The optima I had in there was 2-3 years old and was getting soft.)
A couple of months ago, I discovered the ls2 tb adapter harness had been worn through by a pulley to the point that a couple of wires were exposed. I cut, soldered and shrinkwrapped those, but now that I'm getting P1120 on hot starts, I'm wondering if the sensor got damaged somehow?
I have not cleaned any of the pcm connections or grounds other than the engine bay. Heck, I've even done the big three upgrade even with the stock radio hoping that would clear up the alternator code.
I'd sure appreciate any pointers....
Thanks,
Dan
Burning Brakes
Joined: Aug 2006
Posts: 1,217
Likes: 5
From: Stark County Ohio
I just saw this thread so I thought that I woud post the following from the service manual. It may help someone else.
DTC P1120 Throttle Position (TP) Sensor 1 Circuit
Refer to Cell 20: TP and APP Sensors for complete circuit details.
Circuit Description
The throttle position (TP) sensor is mounted on the throttle body assembly. The sensor is actually 2 individual TP sensors within one housing. Two separate signal, ground and 5 volt reference circuits are used in order to connect the TP sensor assembly and the throttle actuator control (TAC) module. The 2 sensors have opposite functionality. The TP sensor 1 signal voltage increases as the throttle opens, from below 1.0 volt at 0 percent throttle to above 3.5 volts at 100 percent throttle. The TP sensor 2 signal voltage decreases from around 3.8 volts at 0 percent throttle to below 1.0 volt at 100 percent throttle. Also observe that the signal circuit for TP Sensor 1 is pulled up to 5 volts and that the signal circuit for TP Sensor 2 is referenced to ground within the TAC module.
Conditions for Running the DTC
DTCs P0606, P1517, P1518 are not set.
The ignition switch is in the crank or run position.
The ignition voltage greater than 5.23 volts.
Conditions for Setting the DTC
TP sensor 1 voltage is less than 0.13 volts or greater than 4.87 volts.
All of the above conditions met for less than 1 second.
Action Taken When the DTC Sets
The PCM stores the DTC information into memory when the diagnostic runs and fails.
The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.
The TAC system operates in reduced engine power mode. If certain TAC system DTCs are set at the same time, the TAC system may command the engine to shut down.
Conditions for Clearing the MIL/DTC
The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Use a scan tool in order to clear the MIL and the DTC.
Diagnostic Aids
Important
Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A . Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Wiring Systems.
Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component conditions can be located.
The APP sensor 1 and the TP sensor 1 5.0 volt reference circuits are internally connected within the TAC module.
The APP sensor 2 and the TP sensor 2 5.0 volt reference circuits are internally connected within the TAC module.
When the TAC module detects a condition within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.
For an intermittent, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
Disconnect the Throttle Actuator connector before inserting fingers into the throttle bore. After you complete diagnosis, install the air inlet duct to the throttle body.
This step is testing for a short to voltage on the signal circuit.
This step verifies that 5.0 volts is available to the TP sensor 1 5.0 volt reference circuit.
This step is testing for a short to voltage on the 5.0 volt reference circuit.
The APP sensor 1 and the TP sensor 1 share a common 5 volt reference circuit. This step tests the APP sensor 1 for a short to B+.
When the TAC module detects a problem within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing the captured DTC information.
DTC P1120 Throttle Position (TP) Sensor 1 Circuit
Refer to Cell 20: TP and APP Sensors for complete circuit details.
Circuit Description
The throttle position (TP) sensor is mounted on the throttle body assembly. The sensor is actually 2 individual TP sensors within one housing. Two separate signal, ground and 5 volt reference circuits are used in order to connect the TP sensor assembly and the throttle actuator control (TAC) module. The 2 sensors have opposite functionality. The TP sensor 1 signal voltage increases as the throttle opens, from below 1.0 volt at 0 percent throttle to above 3.5 volts at 100 percent throttle. The TP sensor 2 signal voltage decreases from around 3.8 volts at 0 percent throttle to below 1.0 volt at 100 percent throttle. Also observe that the signal circuit for TP Sensor 1 is pulled up to 5 volts and that the signal circuit for TP Sensor 2 is referenced to ground within the TAC module.
Conditions for Running the DTC
DTCs P0606, P1517, P1518 are not set.
The ignition switch is in the crank or run position.
The ignition voltage greater than 5.23 volts.
Conditions for Setting the DTC
TP sensor 1 voltage is less than 0.13 volts or greater than 4.87 volts.
All of the above conditions met for less than 1 second.
Action Taken When the DTC Sets
The PCM stores the DTC information into memory when the diagnostic runs and fails.
The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.
The TAC system operates in reduced engine power mode. If certain TAC system DTCs are set at the same time, the TAC system may command the engine to shut down.
Conditions for Clearing the MIL/DTC
The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Use a scan tool in order to clear the MIL and the DTC.
Diagnostic Aids
Important
Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A . Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Wiring Systems.
Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component conditions can be located.
The APP sensor 1 and the TP sensor 1 5.0 volt reference circuits are internally connected within the TAC module.
The APP sensor 2 and the TP sensor 2 5.0 volt reference circuits are internally connected within the TAC module.
When the TAC module detects a condition within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.
For an intermittent, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
Disconnect the Throttle Actuator connector before inserting fingers into the throttle bore. After you complete diagnosis, install the air inlet duct to the throttle body.
This step is testing for a short to voltage on the signal circuit.
This step verifies that 5.0 volts is available to the TP sensor 1 5.0 volt reference circuit.
This step is testing for a short to voltage on the 5.0 volt reference circuit.
The APP sensor 1 and the TP sensor 1 share a common 5 volt reference circuit. This step tests the APP sensor 1 for a short to B+.
When the TAC module detects a problem within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing the captured DTC information.
