how to diagnose P0301 code in BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools and ensure you have access to the engine bay.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket.
• Remove the ignition coil from cylinder 1 by unscrewing the retaining bolt and pulling it out.
• Use the spark plug socket to remove the old spark plug.
• Inspect the spark plug for signs of fouling or damage.
• Install the new spark plug, ensuring it is gapped correctly to the manufacturer's specifications (typically 0.030 inches).
• Torque the spark plug to the specified value (usually around 15-20 Nm).

3. Replace Ignition Coil

• If the ignition coil is faulty, replace it with a new one.
• Reinstall the ignition coil onto the spark plug and secure it with the retaining bolt.

4. Inspect and Replace Fuel Injector (if necessary)

• Disconnect the fuel injector connector and remove the injector using the appropriate tool or by gently prying it out.
• Inspect for clogs or leaks. If faulty, replace with a new injector.
• Reinstall the new injector and reconnect the fuel injector connector.

5. Perform a Compression Test (if required)

• If compression is low, further engine diagnostics may be necessary.
• Follow manufacturer specifications for compression readings.