All codes › P0304
P0304: Cylinder 4 Misfire Detected
What it means
The engine computer counted repeated misfires in cylinder 4: that cylinder isn't firing properly, so the engine shakes and fuel goes unburned into the exhaust.
Severity: High Cylinder 4 misfire; reduce driving until fixed.
Common causes
- Worn spark plug in cylinder 4
- Failed ignition coil on cylinder 4 (swap it with a neighbor to test)
- Clogged or leaking cylinder 4 fuel injector
- Vacuum leak near cylinder 4's intake runner
- Low compression in cylinder 4 (valve or ring problem)
Most common causes first. Exact causes vary by make, model and engine.
Can I fix it myself?
Often DIY. Coil-swap test; on some engines cylinder 4 sits near the firewall.
Repair cost
SEEDED ESTIMATE Roughly $70–$400
Most likely repair: ignition coil. Diagnosis fees, taxes and other causes are not included.
| Line | Low | High | Basis |
|---|---|---|---|
| Ignition coil | $24 | $155 | Typical listed retail range, source (8-coil kits ~$378–$474 excluded) |
| Labor 0.5–1.5 hr | $50 | $240 | $100–$160/hr, shop survey |
⚠️ This is an editorial placeholder range for this type of repair. It is not based on real invoices or licensed pricing data yet. Real ranges will appear here once enough reader invoices for P0304 are verified.
Verified reader invoices for P0304: 0. Share your repair bill to help build real costs.
Tools that can read P0304
- ScanFixAI: Pro $29.99/mo or $249.99/yr
- OBDAI: Annual PRO bundle $299
- BlueDriver Pro Next-Gen: $119.95 list ($99.95 sale seen)
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