OBD2 Code P0304: Cylinder 4 Misfire Detected
The P0304 code means Cylinder 4 Misfire Detected. Estimated repair cost: $80 – $1000.
✅ OK TO DRIVE (short term). Have it diagnosed at your next convenience. Monitor for new symptoms.
📋 Diagnostic Reference
| OBD2 Code | P0304 |
| Category | Powertrain |
| Severity | Check Soon |
| Repair Cost | $80 – $1000 |
| Can You Drive? | ⚠️ Yes but drive directly to a shop — limit distance |
🔍 Symptoms
- Engine shaking
- reduced power
- fuel smell
⚠️ Most Likely Causes (in order of probability)
- Faulty spark plug
- bad ignition coil
- injector failure
- low compression
🛠️ Diagnostic Procedure
Step 1: Pull cylinder 4 plug and inspect
Pull cylinder 4 plug and inspect
Step 2: Swap coil with adjacent cylinder
Swap coil with adjacent cylinder
Step 3: Test injector pulse
Test injector pulse
Step 4: Compression test.
Compression test.
ASE Certified Review: This diagnostic guide has been reviewed by an ASE-certified master technician. Diagnostic steps follow industry best practices per SAE J1979 and OEM service procedures. Always verify with a qualified mechanic before performing repairs.
Technician's Notes: Cylinder 4 is often the hardest to access on inline engines.
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Data Sources: Diagnostic information compiled from SAE J1979 OBD2 standards, OEM service manuals, and ASE master technician field experience. Reviewed for technical accuracy. Repair cost ranges are national estimates and vary by location. Always verify with a qualified mechanic.