P0304: Cylinder 4 is misfiring
Cylinder 4 Misfire Detected
Cylinder 4 is misfiring. If the light is flashing, stop driving and have it towed. If it is steady, get it checked today. Do not run a misfiring engine longer than you have to.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0304 means cylinder 4 is not combusting properly. On a four-cylinder engine, cylinder 4 is the farthest from the engine's ancillary components, and its coil and injector harnesses are often routed around hot or sharp-edged areas. A misfire here produces the same exhaust risk as any other cylinder misfire: unburned fuel in the exhaust that overloads the catalytic converter. On V6 and larger engines, cylinder 4 is often closer to the firewall, where heat soak and tight spaces make access and diagnosis slower.
Common causes
- Failed ignition coil on cylinder 4Swap the coil with another cylinder to confirm. Coil failure is the most statistically common cause.
- Worn or damaged spark plug on cylinder 4Check the electrode. A worn or cracked plug often causes intermittent misfires that worsen over time.
- Cylinder 4 fuel injector failureElectrical fault or clogging. Check for P0204 in the code list.
- Low compression on cylinder 4Burned valve or worn rings. Compression test is definitive.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Spark plug set
- Ignition coil (one)
- Fuel injector (one)
- Compression repair
Symptoms
- Check engine light flashing or steady
- Rough idle and vibration
- Hesitation and power loss
- Fuel economy drop
- Possible P0204 injector fault alongside this code
What to do next
Start by swapping the cylinder 4 coil with cylinder 3. If the misfire moves to cylinder 3, replace the coil. If it stays on cylinder 4, check the plug. On tight-access V-engines, getting to cylinder 4 may require removing intake components. Budget extra labor if the cylinder is buried. Do not skip the compression test if ignition parts check out clean.
Lewis reads P0304 alongside any other misfire and ignition-related codes, so you can see whether cylinder 4 is isolated or part of a bigger ignition problem. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- I replaced the spark plugs and the misfire came back on cylinder 4. What next?
- Swap the ignition coil. If the misfire follows the coil, that is your answer. If not, check the injector and then compression.
- On a V6, where is cylinder 4?
- V6 cylinder numbering varies by manufacturer. On many GM V6 engines, cylinder 4 is the front cylinder on the passenger bank. Check your engine diagram.
- Can a bad crankshaft sensor cause P0304 on just one cylinder?
- Unlikely. A bad crank sensor causes random or multiple misfires across all cylinders, which would set P0300. A single-cylinder code almost always points to that cylinder's specific components.
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