P0304 is a diagnostic trouble code observed when the is a dictation of misfire in cylinder 4. This code may be seen with other misfire codes and lean / rich codes.
What the P0304 code Is
The P0304 code will be observed in cars where the ECU has detected that cylinder 4 is not firing normally. The ECU monitors the operation of all cylinders to be sure they are all firing on time, so when one misfires repeatedly, a Check Engine Light is set.
What Is cause the P0304 code?
- Faulty spark plug
- Faulty plug wires, cap and rotor, and/or coil pack
- Mechanical engine issue
- Intake leak
- Fuel issues
What are the signs of the P0304 code?
- Engine functioning poorly or having trouble staying running
- Check Engine Light present
- Lack of engine power
- Decreased fuel mileage
How does a mechanic diagnose the P0304 code?
- The mechanic will start by hooking up a scan tool to the DLC port to know which codes are present.
- Freeze frame data will be linked with every code found and should be noted for use on the test drive.
- The codes will now be cleared and a road test carried out under similar conditions to the freeze frame data from earlier.
- Next, a visual inspection will be carried out looking for damaged wires, worn or broken components, or visible leaks.
- Next, the scan tool will be used to monitor the misfire counter for cylinder 4.
- Then, the scan tool will be used to look at the long-term fuel trims to see if fuel issues are availabe and the intake air pressure inspected to see if vacuum leaks are present.
Common mistakes when diagnosing the P0304 code
Mistakes can be made when parts are not tested or when unnecessary components are replaced. To avoid this, follow all steps without skipping any. Replacing the spark plugs and wires fixes this issue for most car. However, the entire system must be tested before knowing what to repair.
How serious is the P0304 code?
P0304 should not stop the vehicle from being driven to a safe location once signs start. With the potential for drivability problems linked with this code, it is advised to have it fixed as soon as possible for safe car operation.
What repairs can fix the P0304 code?
- Spark plugs replacement
- Replacement of cap & rotor,coil pack,plug wire(depending on vehicle)
- Repair of engine mechanical issues
- Fixing air leaks
- Repair of fueling faults
Additional comments for consideration regarding the P0304 code
Coil pack made vehicles with higher mileage may notice coil pack failure. An easy way to test if the coil itself is at fault is to move the suspect coil pack to another cylinder. Then test drive the car to see if the code changes to the new cylinder. If it does, then the coil pack itself has failed.
Depending on year, car will be equipped with either coil packs which are the most modern, spark plug wires which are a little bit older, or a distributor cap and rotor which is often on carbureted vehicles. All of these are considered wear items, and are prone to failure on higher mileage cars. The spark plug wires and cap and rotor are items that are generally changed along with spark plugs at routine intervals.
An advanced level scan tool will required to properly diagnose P0304 – one that does not just simply read the code, but offers access to live engine data. This data will be required to track misfires and see both fuel and intake information.