how to resolve the P0301 misfire code in my BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal.
• Allow the engine to cool before starting the work.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket
• Remove the ignition coil by unbolting it and disconnecting the electrical connector.
• Extract the old spark plug using a spark plug socket.
• Inspect the spark plug for wear; replace it if it shows signs of damage or excessive wear.
• Install the new spark plug and torque it to the manufacturer's specification (usually around 22 lb-ft for BMW).
• Reconnect the ignition coil.

3. Replace Ignition Coil

• If the spark plug replacement does not resolve the issue, proceed to check or replace the ignition coil.
• Disconnect the ignition coil connector and remove the coil from the cylinder head.
• Install the new ignition coil and ensure it is seated correctly.
• Reconnect the ignition coil connector.

4. Replace Fuel Injector (if necessary)

• If the ignition system checks out, check the fuel injector operation.
• Disconnect the fuel line and electrical connector from the fuel injector.
• Remove the fuel injector from the rail and replace it with a new one.
• Reinstall the fuel rail and reconnect all lines and connectors.

5. Final Checks

• Reconnect the negative battery terminal.
• Clear any fault codes using the OBD-II scanner.
• Start the engine and check for any misfire codes again.