Possible Causes
NOTE: The listed causes may not be a complete list of all potential issues and there may be other causes.
- Faulty cylinder 1 ignition coil
- Cylinder 1 ignition coil harness is open or shorted
- Poor electrical connection in cylinder 1 ignition coil circuit
- Faulty Engine Control Module (ECM)
Description
The Engine Control Module (ECM) must determine if a misfire is occurring and identify the specific cylinder(s) and severity of the misfire event, and whether it is relevant for emissions or damaging to the catalyst. To accomplish these tasks, the control module monitors the crankshaft for acceleration losses during the firing segments of each cylinder according to the firing order.
The calculation of engine misfire/roughness is derived from differences in period duration (T) of individual increment gear segments. Each segment period consists of an angular range of 120° of crankshaft angle that begins 78° before Top Dead Center (TDC).
If the expected period duration exceeds the allowed value, a misfire fault for that particular cylinder is recorded in the ECM’s fault memory. Depending on the measured misfire rate level, the control unit illuminates the “Service Engine Soon” light, may cut fuel to the particular cylinder, and may switch lambda operation to open loop. All misfire faults are weighted to determine whether the misfire is relevant for emissions or damaging to the catalyst.
How to Repair
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
- Engine Light On (or Service Engine Soon Warning Light On)