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

Solution

1. Preparation

• Gather necessary tools and ensure the vehicle is parked on a flat surface.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Spark Plug

• Tools Required: Spark plug socket, ratchet, torque wrench.
• Remove the ignition coil from cylinder 1:
  • Disconnect the electrical connector from the ignition coil.
  • Remove the mounting bolt and gently pull the coil out.
• Remove the spark plug:
  • Use a spark plug socket to unscrew the spark plug from the cylinder head.
• Inspect the spark plug for signs of wear, fouling, or damage.
• Replace the spark plug with a new one, ensuring it is gapped correctly according to manufacturer's specifications.
• Reinstall the ignition coil.

3. Inspect and Replace Ignition Coil (if necessary)

• If the ignition coil appears damaged or faulty during inspection:
  • Remove the ignition coil as previously described.
  • Install a new ignition coil in place of the old one.
  • Ensure all connections are secure.

4. Test Fuel Injector

• Tools Required: Multimeter or injector tester.
• Disconnect the fuel injector connector for cylinder 1.
• Check the resistance of the injector using a multimeter (consult specifications for acceptable range).
• If the injector is faulty, replace it with a new one:
  • Remove the old injector carefully from its rail.
  • Install the new injector and reconnect the electrical connector.

5. Check for Vacuum Leaks

• Inspect hoses and gaskets for leaks near the intake manifold.
• If any leaks are found, replace the faulty hoses or gaskets.