What does P0304 mean on my car?

P0304 tells you that the engine control module has detected repeated misfires on cylinder 4. The ECU counts misfires by monitoring tiny variations in crankshaft speed and flags the code when cylinder 4 misfires exceed the allowed threshold.

Is cylinder 4 hard to access?

It depends on how the engine is mounted. On a longitudinal inline-4, usual in rear-wheel-drive cars, cylinder 4 is the one nearest the firewall. On a transverse inline-4, usual in front-wheel-drive cars, the cylinders run across the car and cylinder 4 is at the gearbox end. Access can be tighter on some engines; you may need to remove an engine cover or intake components.

Can a P0304 misfire damage my engine?

The misfire itself does not usually damage the engine block, but unburned fuel washing the cylinder walls can dilute oil and accelerate ring wear over time. The bigger immediate risk is catalytic converter damage from overheating.

Why did P0304 appear after changing spark plugs?

This is usually caused by an incorrectly gapped plug, the wrong plug type for your engine, a plug not seated properly, or a damaged ignition coil boot. Remove the cylinder 4 plug, verify the gap and part number, and re-seat it.

Should I replace all ignition coils if only cylinder 4 is misfiring?

It is not strictly necessary, but if the vehicle has high mileage (over 100,000 km) and the other coils are original, replacing the full set is a good preventive measure. Coils of the same age tend to fail in sequence.

P0304: Cylinder 4 Misfire Detected

Quick Answer

Not safe to drive

P0304 means your engine's computer has identified consistent misfires in cylinder 4. Where cylinder 4 sits depends on how the engine is mounted: on a lengthwise (longitudinal) inline-4, usual in rear-wheel-drive cars, it is the cylinder nearest the firewall, while on a transverse engine, usual in front-wheel-drive cars, it is at the gearbox end. The fault is isolated to that cylinder's ignition, fuel, or compression system.

Severity: High · Misfire
Estimated repair cost: From €35 to €2100+, varies by vehicle

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What does P0304 mean?

P0304 is a misfire-related diagnostic trouble code classified as high severity. When your vehicle's ECU detects this condition, it stores P0304 and illuminates the check engine light.

What are the symptoms of P0304?

If your vehicle has triggered P0304, you may notice one or more of these symptoms:

Check engine light steady or flashing
Rough idle with a noticeable miss
Vibration through the vehicle body at idle
Loss of power when accelerating
Increased fuel consumption
Raw fuel smell from the tailpipe

What causes P0304?

Here are the most common causes of P0304:

Failed ignition coil on cylinder 4
: high
Worn or fouled spark plug on cylinder 4
: high
Clogged or electrically failed fuel injector on cylinder 4
: medium
Intake manifold gasket leak near cylinder 4
: medium
Low compression from burnt exhaust valve or worn rings on cylinder 4
: low

Is it safe to drive with P0304?

No - address this immediately. A persistent misfire on cylinder 4 will damage the catalytic converter and may cause sudden power loss. Do not ignore a flashing check engine light. Have the vehicle diagnosed as soon as possible.

How do you diagnose P0304?

Follow these steps to pinpoint the root cause of P0304:

Retrieve freeze-frame data and note any companion misfire codes (P0300-P0303) that may indicate a wider problem
Swap the ignition coil from cylinder 4 with cylinder 1 or 2, clear codes, and test drive. If the misfire code follows the coil, replace it
Remove and inspect the spark plug on cylinder 4. On a longitudinal inline-4 it is nearest the firewall, on a transverse one it is at the gearbox end, and a spark plug socket with an extension may be needed
Verify the fuel injector on cylinder 4 is receiving its electrical pulse using a noid light. Also check for visible fuel leaks at the injector seal
If ignition and fuel are ruled out, perform a compression and leak-down test on cylinder 4 to check for valve seating issues or ring wear

How much does P0304 cost to fix?

Repair costs for P0304 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Replace spark plug (cylinder 4)	€5–€25	€30–€100	€35–€125	Easy
Replace ignition coil (cylinder 4)	€25–€130	€30–€110	€55–€240	Easy
Replace fuel injector (cylinder 4)	€50–€200	€70–€220	€120–€420	Moderate
Valve or compression repair	€200–€700	€400–€1400	€600–€2100	Professional

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

Engines known for this code

P0304 on specific vehicles

P0304 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0304 on Ford

Ford Focus

See Ford-specific causes & cost

Skoda

Skoda Octavia

2005-2024

The 1.8 TSI and 2.0 TSI engines in the Octavia vRS share the EA888 platform with the VW Golf GTI. Cylinder 4 on these engines is at the gearbox end and benefits from the same walnut blasting maintenance to prevent carbon misfire issues.

P0304 on Mercedes-Benz

Mercedes C-Class

See Mercedes-Benz-specific causes & cost

SEAT

SEAT Leon

2005-2024

The Leon shares VW Group EA211 and EA888 engines. The 1.4 TSI (EA211) in Mk3 models can develop ignition coil failures on any cylinder. Cylinder 4 misfires on the 2.0 TSI Cupra are often traced to carbon buildup from high-performance driving.

These codes are often seen alongside P0304 or indicate related issues:

Common questions about P0304

What does P0304 mean on my car?: P0304 tells you that the engine control module has detected repeated misfires on cylinder 4. The ECU counts misfires by monitoring tiny variations in crankshaft speed and flags the code when cylinder 4 misfires exceed the allowed threshold.
Is cylinder 4 hard to access?: It depends on how the engine is mounted. On a longitudinal inline-4, usual in rear-wheel-drive cars, cylinder 4 is the one nearest the firewall. On a transverse inline-4, usual in front-wheel-drive cars, the cylinders run across the car and cylinder 4 is at the gearbox end. Access can be tighter on some engines; you may need to remove an engine cover or intake components.
Can a P0304 misfire damage my engine?: The misfire itself does not usually damage the engine block, but unburned fuel washing the cylinder walls can dilute oil and accelerate ring wear over time. The bigger immediate risk is catalytic converter damage from overheating.
Why did P0304 appear after changing spark plugs?: This is usually caused by an incorrectly gapped plug, the wrong plug type for your engine, a plug not seated properly, or a damaged ignition coil boot. Remove the cylinder 4 plug, verify the gap and part number, and re-seat it.
Should I replace all ignition coils if only cylinder 4 is misfiring?: It is not strictly necessary, but if the vehicle has high mileage (over 100,000 km) and the other coils are original, replacing the full set is a good preventive measure. Coils of the same age tend to fail in sequence.

Read our detailed guides

Scan your car with Skanyx to diagnose P0304

Your car logged P0304. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €35-€2100 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.