P0304 Cylinder 4 misfire detected
What P0304 means
The engine computer watches crankshaft speed and notices when one cylinder fails to fire properly. P0304 means cylinder 4 is misfiring often enough to raise emissions or risk catalyst damage. On a four-cylinder engine this is usually the cylinder at the gearbox end, but numbering varies by engine.
P0304 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- High
- Typical repair cost
- 40–400 €
- Workshop time
- 0.3–4 h
- Repair difficulty
- Easy
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on or flashing
- Rough idle and vibration
- Hesitation or jerking when accelerating
- Higher fuel consumption
Common causes
- Worn or fouled spark plug in cylinder 4
- Faulty ignition coil for cylinder 4
- Clogged or faulty injector for cylinder 4
- Vacuum leak near cylinder 4's intake port
- Low compression in cylinder 4
Can I keep driving with P0304?
Have it checked today or tomorrow, and avoid hard acceleration. If the light is flashing, the misfire is severe and the catalytic converter can be damaged quickly.
What to check first
- Swap the cylinder 4 coil with another cylinder, clear codes and see if the misfire moves
- Remove and inspect the spark plug; replace plugs if worn or at the service interval
- Check the injector connector and injector function for cylinder 4
- Do a compression or leak-down test if the misfire stays on cylinder 4
Related codes
- P0303 Cylinder 3 misfire detected
- P0305 Cylinder 5 misfire detected
- P0302 Cylinder 2 misfire detected
- P0306 Cylinder 6 misfire detected
- P0301 Cylinder 1 misfire detected
- P0307 Cylinder 7 misfire detected
- P0300 Random/multiple cylinder misfire detected
- P0308 Cylinder 8 misfire detected
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
Updated: