P0304 Code: Meaning, Symptoms, Causes & Fixes
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Causes ranked by likelihood
| Cause | Likelihood | DIY difficulty |
|---|---|---|
| Bad spark plug on cyl 4 — Replace and clear. | Most likely | 2/5 |
| Failing coil on cyl 4 — Common after 80k miles. | Possible | 2/5 |
| Carbon-clogged injector — Try injector cleaner first. | Less likely | 2/5 |
Symptoms of P0304
- Idle vibration
- Power loss
- CEL
How to diagnose P0304
- Confirm the code. Read P0304 with an OBD-II scanner and note the freeze-frame data (speed, temperature, load) recorded when it set.
- Check for companion codes. Look for other stored or pending codes such as P0300, P0303 — they often point to one shared root cause.
- Check: Bad spark plug on cyl 4. Replace and clear.
- Check: Carbon-clogged injector. Try injector cleaner first.
- Check: Failing coil on cyl 4. Common after 80k miles.
- Clear and verify. After the repair, clear the code and complete a full drive cycle to confirm P0304 does not return.
Can I drive with P0304?
Avoid driving with a flashing CEL.
Related codes
Related symptoms
Frequently asked questions
What does P0304 mean?
P0304 means cylinder 4 misfire detected. P0304 means cylinder 4 is misfiring. On 4-cylinder engines this is often the rear-most cylinder — start with spark plug and coil diagnosis.
Can I drive with code P0304?
Avoid driving with a flashing CEL.
What is the most common cause of P0304?
Bad spark plug on cyl 4 — Replace and clear.
What are the symptoms of P0304?
Idle vibration, Power loss, CEL.
How much does it cost to fix P0304?
A typical shop repair range is $30–$600, depending on which cause it turns out to be. Cheaper causes such as carbon-clogged injector should be ruled out first.