Code P0300, Misfire Detected: Notes

PCM can detect a misfire by monitoring fuel control circuit and cam signal circuit input signals. If a consistently repeated RPM variation is detected indicating a misfire, PCM calculates which cylinder is misfiring by associating crankshaft angle (via cam signal) with RPM variation (fuel control). Misfiring cylinder can then be displayed on Tech 1 as current weak cylinder.

Code P0300 will set when the following conditions are present.

• Codes P0101, P0117, P0118, P0122, P0123, P0125, P0740 or P0502 are not set.
• Engine speed is 525-4775 RPM.
• System voltage is 9-16 volts.
• Engine coolant temperature is between -13°F (-25°C) and 248°F (120°C).
• Throttle angle is steady.
• PCM is detecting a crankshaft RPM variation indicating a misfire sufficient to cause three-way catalytic converter damage or emissions levels to exceed mandated standard.

Code P0300 if set will disable TCC. Code P0300 does not illuminate the Malfunction Indicator Light (MIL).

1. If difficulty is encountered while attempting to isolate misfire, operate vehicle under various engine speeds and loads while monitoring current weak cylinder. This may isolate condition which causes misfire to occur.
2. This test checks PCM injector driver and injector wiring.
3. A spark tester must be used because it is essential to verify adequate available secondary voltage at spark plug (25,000 volts). Spark should jump the tester gap on all 6 leads. This simulates a load condition.
4. Coil tower spark plug wire boots may be damaged if ignition coils are carbon tracked.
5. A faulty coil or ignition control module can be determined by installing a properly operating coil.