Circuit Description

A misfire is determined by the ECM. The ECM uses signals provided by the crankshaft and camshaft position sensors to monitor changes in crankshaft rotation for each cylinder. 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 is set when misfiring of random cylinders is detected during any particular 200 or 1000 revolutions. Possible causes are:

• Ignition system.
• Injector(s).
• Fuel pressure.
• EGR system.
• Engine compression.
• Valve clearance.
• Valve timing.
• Mass Airflow (MAF) sensor.
• Engine Coolant Temperature (ECT) sensor.