P0304: Misfire detected in cylinder 4
Combustion is failing in cylinder 4. The most common causes are a worn spark plug, a faulty ignition coil or an injector that is not spraying well.
| Code | P0304 |
|---|---|
| System | Engine and transmission |
| Group | P03xx, Ignition and misfires |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0304 means
The ECU detects each firing stroke through tiny changes in crankshaft speed. It has found that in cylinder 4 the mixture is not burning properly, or at all, and that unburnt fuel goes into the exhaust and overheats the catalytic converter. How the cylinders are numbered is set by each manufacturer.
Most common causes
- Worn or fouled spark plug in cylinder 4 (on petrol engines)
- Faulty ignition coil on that cylinder, or a damaged boot or lead
- Loose or corroded coil or injector connector
- Dirty, blocked or leaking injector on cylinder 4
- Air leak near that cylinder (intake gasket or vacuum hose)
- Low compression in the cylinder from worn valves or piston rings
Symptoms
- Engine shakes, especially at idle or when accelerating
- Engine warning light on, or flashing if the misfire is severe
- Loss of power and jerking
- Higher fuel use and a fuel smell from the exhaust
Can you drive with P0304?
With care If the light is steady and the engine runs reasonably smoothly, you can drive gently to a workshop. If the light is flashing, stop the car: unburnt fuel can ruin the catalytic converter very quickly.
Open the bonnetthe in-depth explanation
How to check it
If the engine has one coil per cylinder, swap the cylinder 4 coil with a neighbour, clear the code and test: if the misfire moves, the coil is to blame. Many readers show a live misfire counter for each cylinder.
How to read and clear P0304 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0304 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0300 Random or multiple cylinder misfire
- P0301 Misfire detected in cylinder 1
- P0302 Misfire detected in cylinder 2
- P0303 Misfire detected in cylinder 3
- P0305 Misfire detected in cylinder 5
- P0306 Misfire detected in cylinder 6
- P0307 Misfire detected in cylinder 7
- P0308 Misfire detected in cylinder 8
- P0313 Misfire detected with low fuel level
- P0316 Misfire detected on start-up (first 1000 revolutions)
- P0320 Engine speed input (ignition or distributor): circuit fault
- P0321 Ignition or distributor engine speed signal out of range
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: Misfires, catalyst and lambda sensors.
What does code P0304 mean?
The ECU detects each firing stroke through tiny changes in crankshaft speed. It has found that in cylinder 4 the mixture is not burning properly, or at all, and that unburnt fuel goes into the exhaust and overheats the catalytic converter. How the cylinders are numbered is set by each manufacturer.
Can you drive with P0304?
If the light is steady and the engine runs reasonably smoothly, you can drive gently to a workshop. If the light is flashing, stop the car: unburnt fuel can ruin the catalytic converter very quickly.
How do you clear P0304?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0304 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
