P0304 means your engine's computer has identified consistent misfires in cylinder 4. On most inline-4 engines, cylinder 4 is at the rear near the firewall, which can make access slightly harder. The fault is isolated to that cylinder's ignition, fuel, or compression system.
Scan your own car in about 60 seconds: see whether P0304 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android, on any ELM327 adapter.
Get Skanyx freeP0304 means your engine's computer has identified consistent misfires in cylinder 4. On most inline-4 engines, cylinder 4 is at the rear near the firewall, which can make access slightly harder. The fault is isolated to that cylinder's ignition, fuel, or compression system.
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.
If your vehicle has triggered P0304, you may notice one or more of these symptoms:
Here are the most common causes of 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.
Follow these steps to pinpoint the root cause of P0304:
Repair costs for P0304 vary depending on the root cause and your vehicle. Here are typical estimates:
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0304 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
On the 1.6 Ti-VCT and 2.0 Duratec engines, cylinder 4 is at the rear of the engine near the firewall. The 1.0 EcoBoost 3-cylinder does not have a cylinder 4. The 2.0 GDI engine can develop carbon buildup affecting cylinder 4.
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.
The M274 2.0-litre turbo engine in the C200/C250 (W205) has documented issues with ignition coil failures and carbon buildup. Cylinder 4 access is restricted on the W205 due to tight engine bay packaging. Mercedes recommends premium plugs replaced at 60,000 km.
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:
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.
On inline-4 engines, cylinder 4 is typically closest to the firewall at the rear of the engine bay. Access can be tighter, especially for spark plugs and coils. On some vehicles you may need to remove an engine cover or intake components.
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.
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.
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.
A 15 euro Bluetooth adapter and a free phone app read the exact fault code a shop charges 30 to 100 euros to pull. Here is how to do it yourself in 5 minutes.
Fixing a P0300 to P0304 misfire costs 40-250 euros for most cases. Here is how to tell which part failed - plug, coil, or injector - before paying for parts.
Your car shakes at idle, under braking, or at 90 km/h. Here are the nine real causes, which ones an OBD2 scan reads, and what each repair costs.
Engine knocking ranges from a harmless cold-start lifter tick to rod knock that ends an engine. Here is how to tell them apart and what each fix costs.
Your car jerks when accelerating and you feel every stumble through the pedal. Here is what causes it, what each fix costs, and when it is safe to keep driving.
A flashing check engine light means the engine is misfiring right now. Pull over and read the code: the fix is usually $80 to $400, the delay costs $1,500 up.
An unfamiliar symbol just lit up and you need to know whether to stop. Read the colour first, then find your symbol in the table: every one carries its verdict.
Your car logged P0304. Skanyx reads it on any standard Bluetooth OBD2 adapter, 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.
Get Skanyx freeGet the newsletter
New fault-code guides, real repair-cost data and seasonal car-care tips. No spam, unsubscribe anytime.
We only email about car diagnostics content. Privacy Policy