Diagnostic trouble code

P0304 Cylinder 4 Misfire Detected

The PCM detects a misfire on cylinder 4.

Misfire Codes

Read This First

This code identifies the failed diagnostic test or circuit family. Confirm the basic checks before replacing parts, and keep freeze-frame data until the repair is verified.

Common Checks

  • Inspect plug, coil, boot, wire, and injector wiring for cylinder 4.
  • Swap-test ignition parts and check scan-tool misfire counters.
  • Run a compression or leakdown test if the misfire stays put.

Common Repairs

  • Replace the failed ignition or fuel component after confirming the fault.
  • Repair engine mechanical issues if compression is low.

Mustang Notes

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.

Sources

  1. SAE J2012DA Digital Annex of Diagnostic Trouble Code Definitions
  2. 1996 Ford Mustang Owner Guide