OBD · Ignition and combustion

P0304 Cylinder 4 misfire detected

Fix soon

What this code means

P0304 is a generic OBD code shared by all manufacturers since 2001 for petrol and 2004 for diesel. It relates to: ignition and combustion. The code tells you what the ECU measured as abnormal, not necessarily which part to replace.

Severity: Fix soon. Drive gently and as little as possible. The fault can get worse and damage other parts.

Most common causes

  1. Failing ignition coil#1

    A misfire on one cylinder that worsens under load or in damp weather is typical of a coil.

    Garage price: Ignition coil £50 – £140
  2. Worn spark plugs#2
    Garage price: Spark plugs £55 – £190Fix it: Replace your spark plugs
  3. Dirty or faulty injector#3
    Garage price: Diesel injector £245 – £650

Cost of related repairs

Independent garageMain dealer
Ignition coil£50 – £140£60 – £215
Spark plugs£55 – £190£75 – £310
Diesel injector£245 – £650£310 – £975

How to read this code

An OBD scanner plugged into the 16-pin socket under the steering wheel reads and clears codes. Bluetooth models cost £20 to £40. Clearing a code without fixing the fault is pointless: it comes back.

Related problems

Engine cranks but won't startCar judders when acceleratingLoss of power and limp modeWhite smoke from exhaustBlack smoke when acceleratingRough or unstable idle

Frequently asked questions

What does code P0304 mean?

P0304: Cylinder 4 misfire detected. P0304 is a generic OBD code shared by all manufacturers since 2001 for petrol and 2004 for diesel. It relates to: ignition and combustion. The code tells you what the ECU measured as abnormal, not necessarily which part to replace.

Can I drive with code P0304?

Fix soon. Drive gently and as little as possible. The fault can get worse and damage other parts.

How much does it cost to fix P0304?

Ignition coil: £50 – £140, Spark plugs: £55 – £190, Diesel injector: £245 – £650.

How to read this code

An OBD scanner plugged into the 16-pin socket under the steering wheel reads and clears codes. Bluetooth models cost £20 to £40. Clearing a code without fixing the fault is pointless: it comes back.