P0304

What it means

Your engine's computer has detected that cylinder number 4 is not firing correctly, meaning it's not contributing power as it should.

Is it safe to drive?

Driving with a P0304, especially if the Check Engine Light is flashing, can lead to catalytic converter damage from unburnt fuel. It's crucial to diagnose and repair the misfire promptly to avoid more expensive repairs.

Most likely causes

• Faulty Spark Plug (Cylinder 4)

  high

  A worn, fouled, or damaged spark plug in cylinder 4 is a very common cause of a single-cylinder misfire.

• Faulty Ignition Coil or Wire (Cylinder 4)

  high

  A failing ignition coil or damaged spark plug wire specific to cylinder 4 will prevent proper spark delivery.

• Clogged or Faulty Fuel Injector (Cylinder 4)

  medium

  If the fuel injector for cylinder 4 is clogged or not opening/closing correctly, it won't deliver the right amount of fuel.

• Low Compression (Cylinder 4)

  low

  Internal engine issues like worn piston rings, damaged valves, or a blown head gasket affecting cylinder 4 can cause a loss of compression and misfire.

Related help

• Full P0304 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?