Common Checks
- Inspect the cylinder 3 spark plug, coil, boot, and injector connector.
- Swap ignition parts with another cylinder and confirm whether the code follows.
- Check for intake leaks near the affected runner.
Diagnostic trouble code
P0303 Cylinder 3 Misfire Detected
The PCM detects a misfire on cylinder 3.
Misfire CodesCommon Repairs
- Replace the failed ignition or injector component found by testing.
- Repair local intake, wiring, or compression faults if the misfire remains.
Mustang Notes
- Do not clear and ignore a flashing MIL; active misfires can damage catalysts.
Model-Year Applicability
Listed for 1996 and newer traditional gasoline Mustang pages in this first-pass catalog. Engine, calibration, and Ford-specific codes may narrow that range as more service data is added.