Powertrain Controls Diagnosis
CIRCUIT DESCRIPTIONThe powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the 3-way catalytic converter (TWC). The malfunction indicator lamp (MIL) will flash if TWC damaging conditions are present.
CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0125, P0128, P0335, P0336, P0341, P0343, P0502, P0503, P1114, P1115, P1120, P1220, P1221, or P1336 are not set.
^ The engine speed is between 375-5,001 RPM for an automatic transmission.
^ The engine speed is between 450-5,001 RPM for a manual transmission.
^ The ignition voltage is between 10-18 volts.
^ The engine coolant temperature (ECT) is between -7 to +130°C (19-266°F).
^ The fuel level is more than 10 percent.
^ The throttle position (TP) sensor angle is steady within 1 percent.
^ The antilock brake system (ABS) and the traction control system are not active.
^ The transmission is not changing gears.
^ The secondary air injection (AIR) diagnostic test is not in progress (RPO NC1 only).
^ The A/C clutch is not changing states.
^ The PCM is not in fuel shut-off or decel fuel cut-off (DFCO) mode.
^ The ABS signal is not exceeding rough road thresholds.
CONDITIONS FOR SETTING THE DTC
^ The PCM determines that an emission type misfire is present.
^ The PCM determines that a catalyst damaging misfire is present.
ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
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
IMPORTANT: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Verify that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
^ Running the vehicle Out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have fuel level DTCs also set.
^ A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ Excessive vibration from sources other than the engine can cause a misfire DTC. The following are possible sources of vibration:
- Variable thickness brake rotor
- Drive shaft not balanced
- Certain rough road conditions
^ Observe, if more then one cylinder is misfiring, the scan tool may only display one cylinder misfiring. This will not be apparent until the repair is completed. Also, if an ignition coil ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders misfiring. Inspect the ground circuit for the ignition coil on the cylinder bank of the engine that has more then one cylinder misfiring.
TEST DESCRIPTION
Steps 1-2:
Steps 3-5:
Steps 6-12:
Steps 13-19:
The numbers below refer to the step numbers on the diagnostic table.
2. Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.
If the Misfire Current counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. Perform the diagnostic table for DTC P0335 first if this condition is suspected.
If a misfire is present and you suspect a fuel control problem, force the fuel system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.
A misfire may not be apparent at idle. The misfire may only occur above idle under a load. Road test the vehicle and monitor the misfire current counters.
If more than one cylinder is misfiring, the misfire current counters may only increment for one cylinder. Example: Cylinders 1 and 8 are both misfiring, yet only cylinder 8 increments on the misfire current counter.
If one of the injector fuses is open, only two or three misfire current counters may increment for the corresponding side of the engine.
4. The cylinder with the more significant misfire may cause another cylinder counter to increment only by a small amount.
10. If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
12. An engine mechanical problem can cause a spark plug to gas foul. Inspect for loose rockers, collapsed lifters, or worn camshaft lobes.
17. If the customer concern is the MIL flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.