Powertrain Controls Diagnosis

Circuit Description
The Crankshaft Position sensor is mounted through the side of the engine block at the rear of Bank 2 above the starter assembly. The Crankshaft Position sensor works in conjunction with a 24X reluctor wheel on the crankshaft. The reluctor wheel is inside the engine immediately in front of the rear main bearing. The PCM provides a 12 volt power supply to the CKP sensor as well as a ground and a signal circuit.
A misfire causes a change in crankshaft speed. The PCM times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in crankshaft speed has occurred. You can expect a certain amount of acceleration/deceleration between each firing stroke, but if the crankshaft speed changes are greater than an expected amount, the PCM interprets this as a misfire.
The PCM uses the Crankshaft Position sensor for misfire detection and to control spark and fueling. As the crankshaft rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 24X signal in combination with the Camshaft Position sensor 1X signal in order to accurately determine crankshaft position. The PCM also calculates a 4X signal from this information. The PCM uses the 4X signal for internal calculations. The 4X signal also provides a tach signal for any device which requires one.
Observe that as long as the PCM receives the Crankshaft Position sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.

Conditions for Running the DTC
^ DTCs P0101, P0102, P0103, P0117, P0118, P0121, P0122, P0123, P0125, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, P1258 not set.
^ The engine speed is between 375 RPM and 5001 RPM for automatic transmission.
^ The engine speed is between 450 RPM and 5001 RPM for manual transmission.
^ The ignition voltage is between 10.0 volts and 18.0 volts.
^ The engine coolant temperature is between -7°C (19°F) and 130°C (266°F).
^ Fuel level greater than 10%
^ The TP sensor angle is steady within 1%.
^ The ABS and Traction Control systems are not active.
^ The transmission is not changing gears.
^ The 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 mode.
^ The ABS signals 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 PCM illuminates the Malfunction Indicator Lamp (MIL) under the following conditions:
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed.
^ The first time the diagnostic fails, the PCM records the operating conditions in Failure Records.
^ The PCM determines the percent of misfire over a 1000 revolution period is high enough to cause excessive tail pipe emissions. The PCM illuminates the Malfunction Indicator lamp the next consecutive ignition cycle that the diagnostic runs and fails, if the diagnostic fails under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed.
Or
^ The PCM flashes the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails a catalyst damaging misfire.

Conditions for Clearing the MIL/DTC

Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than the three ignition cycles. Review the Freeze Frame/Failure Records for the last failure conditions.

^ The PCM turns the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail within the same conditions that the DTC last failed.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ A last test failed (Current DTC) clears when the diagnostic runs and does not fail.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure 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 could 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 mis-firing, the scan tool may only display one cylinder mis-firing. This will not be apparent until the repair is completed. Also, if an ignition coil/module ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders mis-firing. Inspect the ground circuit for the ignition coil/modules on the cylinder bank of the engine that has more then one cylinder mis-firing.

Test Description
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/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.
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 only 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 cylinders 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. If there are no fuel system problems, 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 customers concern is the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic. Refer to DTC P0420 Catalyst System Low Efficiency Bank 1 and/or DTC P0430 Catalyst System Low Efficiency Bank 2. P0420 P0430