how to fix P0304 code on BMW 3 Series G20/G21 (2019-2024)

BMW 3 Series G20/G21 (2019-2024)

Error Codes

2-4 hours

Time

medium

Difficulty

medium

Severity

Error Code: P0304

4 min read

638 words

Problem Statement

The P0304 code indicates a misfire detected in cylinder 4 of a BMW 3 Series G20/G21 (2019-2024). This can lead to engine performance issues, increased emissions, and potential lon

Error Code

P0304

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical components.
•Allow the engine to cool before opening any components to prevent burns.

Symptoms

•Check engine light illuminated
•Rough idle or uneven engine running
•Loss of acceleration or power
•Increased fuel consumption
•Engine stalling at low RPMs
•Vibrations felt in the cabin

Diagnostic Steps

1
Scan the vehicle's OBD-II system to confirm the P0304 code and check for any additional codes.
2
Inspect the spark plug in cylinder 4 for wear, damage, or improper gap.
3
Test the ignition coil for cylinder 4 for proper operation.
4
Check the fuel injector for cylinder 4 to ensure it is functioning and delivering fuel.
5
Conduct a compression test on cylinder 4 to rule out mechanical issues such as a blown head gasket or valve problems.
6
Inspect vacuum lines and intake manifold for leaks that could affect cylinder performance.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•Remove the spark plug using the spark plug socket and ratchet.
•Inspect the old spark plug for signs of wear, carbon buildup, or damage.
•Torque the spark plug to the manufacturer's specification (typically 15-20 Nm).

Parts Required

•Spark plug (for cylinder 4)
•Ignition coil (if required)
•Fuel injector (if required)

Related Faults

Share this solution

Comments

No comments yet

Be the first to share your thoughts

Back to Generation

Diagnostic Steps

1
Scan the vehicle's OBD-II system to confirm the P0304 code and check for any additional codes.
2
Inspect the spark plug in cylinder 4 for wear, damage, or improper gap.
3
Test the ignition coil for cylinder 4 for proper operation.
4
Check the fuel injector for cylinder 4 to ensure it is functioning and delivering fuel.
5
Conduct a compression test on cylinder 4 to rule out mechanical issues such as a blown head gasket or valve problems.
6
Inspect vacuum lines and intake manifold for leaks that could affect cylinder performance.

Solution

1. Preparation

Gather necessary tools and parts.
Disconnect the negative terminal of the battery to ensure safety.
Allow the engine to cool down before proceeding.

2. Replace Spark Plug

Tools Required: Spark plug socket, ratchet, torque wrench.
Remove the ignition coil from cylinder 4 by unbolting it and disconnecting the electrical connector.
Remove the spark plug using the spark plug socket and ratchet.
Inspect the old spark plug for signs of wear, carbon buildup, or damage.
Install the new spark plug, ensuring it is gapped correctly to the manufacturer's specification (typically around 0.024-0.028 inches).
Torque the spark plug to the manufacturer's specification (typically 15-20 Nm).

3. Check and Replace Ignition Coil (if necessary)

If the spark plug appears fine, test the ignition coil with a multimeter to check for proper resistance.
If defective, remove the ignition coil and install a new one.
Reconnect the electrical connector and secure the coil in place.

4. Inspect and Test the Fuel Injector

Disconnect the fuel injector connector for cylinder 4.
Using a multimeter, test the injector for resistance; it should typically be around 12-16 ohms.
If the injector is faulty, remove it and replace it with a new one.
Reconnect the fuel injector and ensure secure connections.

5. Conduct Compression Test (if misfire persists)

Remove all spark plugs to allow for even crankcase pressure.
Insert the compression tester in the cylinder 4 spark plug hole.
Crank the engine and record the compression reading; it should generally be within the range specified in the service manual (around 120-200 psi).
If compression is low, further diagnosis of engine internals may be necessary (valve seats, head gasket, etc.).