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.
DTC/P0304·Ford
P0304 on Ford: Causes, Symptoms and Fix Cost
Quick Answer
High SeverityNot safe to driveFord
P0304 on a Ford 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.
Repair cost on Ford€35 - €2100
What does P0304 mean on a Ford?
Ford Focus
2005-2022On 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.
What causes P0304 on a Ford?
Beyond the generic causes listed on the main P0304 page, these are the Ford-specific patterns we see most often:
Ford FocusCarbon buildup on 2.0 GDI intake valves
Ford FocusIgnition coil failure on 1.6 Ti-VCT, especially at higher mileage
How to diagnose P0304 on a Ford with OBD2
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 inline-4 engines, cylinder 4 is nearest the firewall, so 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 on a Ford? (EUR)
Estimated repair costs on a Ford (Ford costs align with the average for this code across makes).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0304 on Ford
These codes commonly cluster with P0304 on Ford vehicles:
FAQ: P0304 on Ford
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?
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.
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.
Looking for the full P0304 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0304 guideSkanyx · Ford
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