Note. DTC P0300 is set when the ECM recognizes a general misfire in the engine. If the ECM determines the cylinder causing the misfire it will set a specific DTC P0301-P0308, to indicate the number of the cylinder causing the misfire. If a DTC P0301-P0308 is retrieved, use this procedure to diagnose the misfire condition in the indicated cylinder.
Note. For circuit reference, see the appropriate WIRING DIAGRAMS article. For connector and terminal identification, see CONNECTOR IDENTIFICATION .
Circuit Description
Crankshaft Position (CKP) sensor reluctor (4X) is located on front of crankshaft. CKP sensor will send a pulse on every falling edge of 4X reluctor wheel. A misfire will cause a change in crankshaft speed. PCM times interval between each pulse and compares each new interval with previous one to determine when an excessive change in crankshaft speed has occurred. A certain amount of acceleration/deceleration is expected between each firing stroke, but if crankshaft speed changes are more than expected amount, PCM will interpret this as a misfire. PCM continuously calculates crankshaft position from low and high resolution signals. This information is used to determine which cylinder is misfiring so that PCM can increment appropriate misfire counter.
DTC will set when following conditions are present
- DTCs P0100, P0102, P0103, P0107, P0108, P0117, P0118, P0122, P0123, P0335, P0336, P0500, P0502, P0601 or P0742 not set.
- Engine speed 325-300 RPM.
- Ignition voltage 9-16 volts.
- Engine coolant temperature 19-266°F (-7-130°C).
- Throttle angle steady within one percent.
- ABS and traction control not active.
- Transmission not changing gears.
- EGR and AIR diagnostics not active.
- A/C clutch steady.
- Not in fuel-shutoff or decel fuel cut-off.
- ABS signals not exceeding rough road thresholds.
- PCM determines that an emission-type misfire is present.
- PCM determines that a catalyst damaging misfire is present.