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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• 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:
  1. Unplug the electrical connector from the ignition coil.
  2. Remove the bolts securing the ignition coil and gently pull it out.
• Remove the spark plug:
  1. Use a spark plug socket to unscrew the old spark plug.
  2. Inspect the spark plug for signs of wear or carbon buildup.
• Install the new spark plug:
  1. Apply anti-seize compound to the threads (if required).
  2. Hand-tighten the spark plug, then torque it to 20 Nm (15 ft-lbs).

3. Replace Ignition Coil

• Tools Required: Socket set, torque wrench.
• Install the new ignition coil:
  1. Align the ignition coil with the spark plug and push it down until it clicks.
  2. Secure the ignition coil with the bolts and reconnect the electrical connector.

4. Test Fuel Injector

• Tools Required: Fuel injector tester (or multimeter).
• Test the fuel injector for cylinder 1:
  1. Disconnect the fuel injector connector.
  2. Test the resistance of the injector using a multimeter; it should typically be between 12-16 ohms.
• If faulty, replace the fuel injector:
  1. Remove the fuel rail (if necessary) and replace the injector.
  2. Reinstall the fuel rail and reconnect connectors.

5. Reassembly and Final Checks

• Reconnect the negative battery terminal.
• Clear the error codes using the OBD-II scanner.
• Start the engine and allow it to idle for a few minutes.