P0304 (generic)
Cylinder 4 Misfire Detected
System: Powertrain · Ignition / Misfire
Severity: severe · Inspection: often fails
Description
Cylinder 4 is misfiring. Inspect spark plug, coil, injector, and compression.
Diagnostic snapshot P0304
- Difficulty
- 6/10 — Intermediate diagnostics
- Est. repair cost
- $120 – $450 (parts + typical shop labor)
- Common symptoms
- Misfire or hesitation under load
- Check engine light (MIL)
- Rough idle
- Reduced power / limp mode
Diagnostic workflow
- Confirm P0304 with a live scan — note pending vs stored and freeze frame data.
- Verify reported symptoms: Misfire or hesitation under load, Check engine light (MIL), Rough idle.
- Inspect wiring/connectors and related sensors before replacing modules.
- Most likely fixes: Cylinder-specific misfire diagnosis (swap / compression / injector); Spark plug / coil / ignition diagnosis.
- Clear codes and road-test; re-scan after two drive cycles if the monitor must set.
Topics
- OBD-II and scan tools (guide)
- Powertrain DTCs (P-prefix) (system)
Related symptoms
- Misfire or hesitation under load (weight 0.900)
- Check engine light (MIL) (weight 0.860)
- Rough idle (weight 0.820)
- Reduced power / limp mode (weight 0.420)
Common fixes (curated)
- Cylinder-specific misfire diagnosis (swap / compression / injector) (rank 1)
- Spark plug / coil / ignition diagnosis (rank 2)
Related articles
None published for this code yet.
Diagnostic bundle (JSON)
Machine-readable graph: related codes, symptoms, fixes, topics, articles, and curated sources rows. Append &external=1 for optional YouTube / Google CSE hits when API keys are configured (see web/.env.example).