how to fix a P0304 code on my BMW 3 Series E90/E91 (2005-2012)

BMW 3 Series E90/E91 (2005-2012)

Error Codes

1-3 hours

Time

medium

Difficulty

medium

Severity

Error Code: P0304

3 min read

568 words

Problem Statement

The P0304 code indicates a misfire in cylinder number 4 of a BMW 3 Series E90/E91 (2005-2012). This issue can lead to poor engine performance, increased emissions, and potential e

Error Code

P0304

Estimated Time

1-3 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

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

Symptoms

•Check engine light illuminated
•Rough idle or shaking during engine operation
•Loss of power during acceleration
•Increased fuel consumption
•Engine stalling or difficulty starting
•Unusual noises from the engine compartment

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0304 and check for any additional codes.
2
Inspect spark plugs for wear or damage, particularly the one in cylinder 4.
3
Check ignition coil operation on cylinder 4; swap it with another cylinder to see if the misfire follows the coil.
4
Perform a compression test on cylinder 4 to check for mechanical issues.
5
Inspect fuel injector operation for cylinder 4; listen for clicking sounds during operation.
6
Check for vacuum leaks in the intake manifold or around the engine 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

•OBD-II scanner
•Socket set
•Spark plug socket
•Torque wrench
•Multimeter

Parts Required

•Spark plug (specific for BMW E90/E91)
•Ignition coil (if faulty)
•Fuel injector (if necessary)

Related Faults

Share this solution

Comments

No comments yet

Be the first to share your thoughts

Back to Generation

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0304 and check for any additional codes.
2
Inspect spark plugs for wear or damage, particularly the one in cylinder 4.
3
Check ignition coil operation on cylinder 4; swap it with another cylinder to see if the misfire follows the coil.
4
Perform a compression test on cylinder 4 to check for mechanical issues.
5
Inspect fuel injector operation for cylinder 4; listen for clicking sounds during operation.
6
Check for vacuum leaks in the intake manifold or around the engine that could affect cylinder performance.

Solution

1. Preparation

Gather tools and parts: OBD-II scanner, socket set, spark plug socket, torque wrench, multimeter, and replacement parts as needed.
Ensure the vehicle is parked on a flat surface and the engine is cool.

2. Replace Spark Plug

1.1 Remove the engine cover if applicable.
1.2 Disconnect the battery (negative terminal).
1.3 Remove the ignition coil from cylinder 4 using a socket.
1.4 Remove the old spark plug using a spark plug socket.
1.5 Inspect the spark plug for signs of fouling or wear.
1.6 Install a new spark plug, ensuring it is gapped correctly (typically 0.032-0.036 inches).
1.7 Torque the spark plug to the manufacturer’s specifications (usually around 15-20 lb-ft).
1.8 Reinstall the ignition coil and reconnect the battery.

3. Replace Ignition Coil (if necessary)

2.1 If the ignition coil was suspect, remove it from cylinder 4 and replace it with a new one.
2.2 Reconnect all electrical connections and ensure the coil is seated properly.

4. Check Fuel Injector (if necessary)

3.1 If the misfire persists, inspect the fuel injector for cylinder 4.
3.2 Remove the fuel rail if necessary and replace the injector with a new one.
3.3 Ensure all connections are tight and secure before reassembly.