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.

Code 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.
• Manifold Absolute Pressure (MAP) sensor.
• Coolant Temperature Sensor (CTS).