my BMW 3 Series E90/E91 (2005-2012) has a check engine light and code P0301

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety while working on electrical components.

2. Inspect and Replace Ignition Coil

• Tools Required: Socket set, torque wrench
• Remove the engine cover (if applicable) to access ignition coil.
• Disconnect the electrical connector from the ignition coil.
• Remove the ignition coil bolt with a socket and pull the coil out.
• Replacement: Install a new ignition coil, tightening the bolt to the manufacturer’s specified torque (typically around 10 Nm).
• Reconnect the electrical connector.

3. Inspect and Replace Spark Plug

• Tools Required: Spark plug socket, torque wrench
• Remove the ignition coil as described in the previous step.
• Use a spark plug socket to remove the spark plug from cylinder 1.
• Inspect the spark plug for signs of wear or fouling.
• Replacement: Install a new spark plug, ensuring it is gapped correctly (typically around 0.7-0.8 mm for BMW).
• Use a torque wrench to tighten the spark plug to the specified torque (generally 25 Nm).

4. Inspect and Clean Fuel Injector

• Tools Required: Fuel injector cleaning kit (if using), basic hand tools
• Disconnect the electrical connector from the fuel injector.
• Remove the fuel injector retaining clips and carefully pull out the injector.
• Cleaning: Clean the injector using a fuel injector cleaning solution or replace it with a new one.
• Reinstall the injector, ensuring it is seated properly, and reattach the clips and connector.

5. Reassemble and Test

• Reinstall any components removed during the process, including the engine cover.
• Reconnect the negative battery terminal.
• Start the engine and check for any abnormal sounds or lights.