Diagnostic Aids

Inspect for any of the following conditions:

• If any DTCs other than misfire P0301-P0306 are set, diagnose those DTCs first.
• An intermittent ignition system malfunction may cause DTC P0300 to set. Inspect the ignition system performance with an engine oscilloscope.
• Review the misfire counters located in the Engine Data list of the scan tool while the engine is running. If the Misfire Current Cylinder# data parameter is increasing, the misfire condition is present. Misfire activity can be monitored with the scan tool in the Misfire Current Cyl # data list parameter of the appropriate cylinder. Use this information in order to determine if the fault is present or an intermittent malfunction.
• Inspect for good quality recently purchased fuel. Inferior quality fuel or fuel that has aged can cause poor combustion that results in detectable engine misfire. If the fuel is suspect, drain and replace as necessary.
• An intermittent can also be the result of a defective CKP sensor signal rotor. Inspect the CKP signal rotor for nicks, dents, missing teeth, and foreign material.
• Inspect for engine overheating. Refer to Engine Overheating .

An intermittent malfunction may be caused by a fault in the electrical circuits of the ignition system or fuel system of the misfiring cylinder. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs .

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.