Diagnostic Aids

If any DTCs other than misfire DTCs P0300-P0303 are present, diagnose those DTCs first. Check for engine overheating, vacuum leaks or improper EGR system operation. Ensure PCV valve is operating properly. Check ignition system for a malfunction, including spark plugs, spark plug wires, and ignition coil. Ensure fuel pressure is correct and fuel injectors are operating properly. Water in fuel may cause an intermittent misfire. Check engine mechanical operation, including cylinder compression and valve adjustment function.

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.