Circuit Description

A misfire is determined by the ECM. The ECM uses signals provided by the crankshaft and camshaft position sensors. If the engine speed rate has changed enough to equal a preset number, a misfire is detected and the MIL is illuminated. If the misfire rate is high enough, and driving conditions will cause catalytic converter damage or overheating, the MIL blinks when a misfire is occurring.

DTC P0300 is set when misfiring of random cylinders is detected during any particular 200 or 1000 revolutions of engine. DTC P0301-308 are set when any particular 200 revolutions of engine, misfiring is detected which can cause catalytic converter overheating and/or damage.

DTC P0301-308 are also set when any particular 1000 revolutions of engine, misfiring is detected which can cause a deterioration in emission levels. Possible causes are:

• Ignition system.
• Injector(s).
• Incorrect fuel line pressure.
• Engine compression.
• Valve clearance.
• Valve timing.
• Mass Airflow (MAF) sensor.
• Engine Coolant Temperature (ECT) sensor.
• Open or short in engine wiring.
• Poor connector connection.
• ECM.