What P0304 means
The control module detected a misfire pattern associated with cylinder 4. It does not identify the failed component.
A trouble code identifies a detected condition. Use the surrounding evidence to choose a test instead of treating the code as a failed-part diagnosis.
- 01PreserveCode, module, freeze frame, readiness
- 02ClassifyCylinder 4 Misfire Detected
- 03InspectIgnition or spark-plug concern / Injector, fuel, or mixture concern
- 04TestRecord freeze frame and cylinder counters / Inspect cylinder 4 and recent work
- 05VerifyRepair only when evidence supports it; retest
Follow the sequence, stop when evidence changes the path, and verify the exact vehicle information before acting.
Record every stored and pending code, freeze frame, readiness state, and relevant live data before clearing anything. Companion codes and operating conditions often matter more than the code name.
Symptoms you may notice
- Rough running
- Hesitation
- Reduced power
- Check-engine light
Cause groups to investigate
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Diagnostic route
Record freeze frame and cylinder counters
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Inspect cylinder 4 and recent work
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Compare ignition and injection evidence
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Test mechanical condition when indicated
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Verify under the original conditions
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Common mistakes
- Replacing the cylinder 4 coil from the code aloneA diagnostic trouble code identifies a detected condition; it does not automatically identify the failed part.
- Ignoring companion mixture or timing codesA diagnostic trouble code identifies a detected condition; it does not automatically identify the failed part.
Sources and verification
The standardized code meaning is tied to SAE J2012. Additional government sources may document the monitor family or public code description. Cause groups and diagnosis remain general guidance; manufacturer-enhanced definitions, enable criteria, test values, and exact procedures require authoritative information for the vehicle.