Definition of the P0304 code
P0304 is a diagnostic trouble code that appears when an ignition error is detected on cylinder 4. This code can be seen with other ignition error codes and poor/deficient codes.
What the P0304 code means
The P0304 code will be seen on cars where the ECU has detected that cylinder 4 is not firing correctly. The ECU monitors the operation of all cylinders to ensure that they all fire on time, so when one of them fails repeatedly, the Check Engine light will come on.
What causes the P0304 code?
- Spark plug defective
- Faulty spark plug wires, spark plug, and rotor and/or ignition coil package.
- Mechanical problem with the engine
- Intake leak
- Fuel problems
What are the symptoms of code P0304?
- The motor runs poorly or has difficulty continuing to run
- Check engine light comes on
- Fire Fault
- Lack of engine power
- Reduced fuel consumption
How can a mechanic diagnose a P0304 code?
- The mechanic will begin by connecting a scan tool to the DLC port to determine what codes are present.
- Frozen frame data is associated with each code found and should be noted for use during the test drive.
- The codes will be erased, and a road test will be performed under similar conditions as the previous data freeze.
- This should be followed by a visual inspection for damaged wiring, worn or damaged components, or visible leaks.
- Next, use a scan tool to check the cylinder 4 ignition fault counter.
- The scan tool will then be used to review the long-term fuel coating for fuel problems and the intake air pressure is checked for vacuum leaks.
Most common errors when diagnosing the P0304 code
Errors can be made when components are not checked or when unnecessary components are replaced. To avoid this, follow all the steps without skipping any. Replacing spark plugs and wires solves the problem in most vehicles. However, test the entire system before determining what should be repaired.
How serious is the P0304 code?
- The P0304 code should not prevent you from driving your vehicle to a safe location after experiencing symptoms. Due to the potential driving problems associated with this code, it is recommended that it be repaired as soon as possible to ensure safe operation of the vehicle.
- What repairs can repair a P0304 code?
- Spark Plug Replacement
- Cover and rotor replacement, coil pack, spark plug wires (depending on vehicle)
- Repair of engine mechanical problems
- Repair Air Leaks
- Repair Fuel Failures
Additional notes on code P0304
Vehicles equipped with higher mileage coil packs may have a failed coil pack. An easy way to find out if the coil pack itself is to blame is to reposition the suspect coil pack to another cylinder. Then test the vehicle to see if the code changes on the new cylinder. If it does, the coil packing itself is damaged.
Depending on the year, vehicles will have coils that are state of the art, slightly older spark plug wires, or a distributor cap and rotor that is usually found on carbureted vehicles. All of these components are considered to be worn out and prone to failure in higher mileage vehicles. The spark plug wires and the cap and rotor are components that are usually replaced along with the spark plugs at routine intervals.
In order to properly diagnose P0304, an advanced level scan tool is needed – a tool that not only reads the code, but gives access to current engine data. This data will be needed to track fires and view fuel and intake information.
