Circuit/System Description

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the crankshaft position (CKP) sensor (POS) signal to vary, the ECM can determine that a misfire is occurring.

When a misfire condition occurs that can damage the three way catalyst due to overheating, the MIL will blink on the first trip. When a misfire condition occurs, the ECM monitors the CKP sensor signal every 200 engine revolutions for a change.

For misfire conditions that will not damage the three way catalyst (but will affect vehicle emissions), the MIL will only light when the misfire is detected on a second trip. During this condition, the ECM monitors the CKP sensor signal every 1, 000 engine revolutions. A misfire malfunction can be detected on any one cylinder or on multiple cylinders.