Test Description

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2
   
   A misfire may not be apparent at idle. The misfire may only occur above idle or under a load. Road-test the vehicle, and monitor the Misfire Current Counters.

   If certain DTCs set at the same time or after DTC P0300 sets, the Misfire Current Counters will not increment. Refer to conditions for running DTC P0300 for the applicable DTC list.

   If more than one cylinder is misfiring, the Misfire Current Counters may increment for only one cylinder. For example, cylinder 1 and cylinder 8 are both misfiring, but only Cylinder 8 increments on the Misfire Current Counter.

   If one injector fuse is open, only 2 or 3 Misfire Current Counters may increment for the corresponding side of the engine.

   Wetting the secondary ignition system with water from a spray bottle may help to locate the damaged or deteriorated components. When you apply the water, look and listen for arcing or misfiring.

   If the Misfire Current Counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. If you suspect that this condition exists, perform the diagnostic test for DTC P0335 first. See DTC P0335: CRANKSHAFT POSITION SENSOR CIRCUIT .

   If a misfire is present and you suspect a fuel control condition, force the fuel system into Open Loop using the scan tool, and allow the engine to run for a few minutes. If this procedure eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.

2. 4
   
   The cylinder with the more significant misfire may cause another cylinder's counter to increment by only a small amount.
3. 10
   
   If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
4. 12
   
   If you cannot locate a fuel system condition, check engine mechanical condition. An engine mechanical condition can cause a spark plug to gas foul. Inspect for loose rockers, and inspect for collapsed lifters or for worn camshaft lobes. See appropriate article in ENGINES.
5. 17
   
   If the customer's concern is that the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.