Circuit Description

ECM uses signals provided by crankshaft and camshaft position sensors. If engine speed rate has changed enough to equal a preset number, a misfire is detected and MIL is illuminated. If misfire rate is high enough, and driving conditions will cause catalytic converter damage or overheating, MIL blinks when a misfire is occurring. DTC is set during any particular 200 revolutions of engine during which misfiring is detected which can cause catalytic converter overheating and/or damage, or during any particular 1000 revolutions of engine during which misfiring is detected which can cause a deterioration in emission levels. Possible causes are:

• Open or short in wiring.
• Poor contact at ECM or component.
• Disconnect, blocked or damaged vacuum hose(s).
• Ignition system malfunction.
• Defective fuel injector(s).
• Improper fuel pressure.
• Defective EGR system.
• Defective Manifold Absolute Pressure (MAP) sensor.
• Defective Engine Coolant Temperature (ECT) sensor.
• Improper engine compression.
• Improper valve clearance.
• Improper valve timing.
• Defective ECM.