Diagnostic Aids

If a fuel injector DTC is set, diagnose that DTC first.

PCM will set a DTC P0300 first, even if a specific cylinder is misfiring. If a specific cylinder misfires for a certain length of time, a specific cylinder misfire will then set.

If vehicle has had a prior replacement of a PCM or crankshaft sensor, crankshaft must be relearned. Perform CRANKSHAFT POSITION VARIATION LEARN PROCEDURE under PROGRAMMING.

Torque converter may be momentarily disabled to determine if misfire was due to a rough road (A/T).

NOTE: History counters will only store counts when MIL is commanded on.

Use scan tool DATA DISPLAY information to check MISFIRE HISTORY CYL. #1-4 to determine whether engine had a specific or random misfire.

Check ignition system for a malfunction, including spark plugs, spark plug wires, and ignition coil. Ensure injector resistance is 12-13 ohms, spark plug gap is 0.045" (1.1 mm), primary ignition coil resistance is 0.4-1.6 ohms and secondary coil resistance is 3.8-5.1 k/ohms.

Check for conditions or faulty components which could cause an engine misfire. See appropriate TROUBLE SHOOTING - NO CODES article. An intermittent malfunction may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, or poor terminal-to-wire connections before component replacement.