how to diagnose P0302 misfire code in BMW 3 Series E90/E91 (2005-2012)?

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Replace Spark Plug

• Remove the engine cover if applicable.
• Disconnect the ignition coil from the electrical connector.
• Remove the ignition coil from cylinder 2 by pulling it straight out.
• Unscrew the spark plug using a spark plug socket and ratchet.
• Install a new spark plug, ensuring it is gapped to manufacturer specifications (typically 0.028-0.032 inches for BMW).
• Reinstall the ignition coil and reconnect the electrical connector.

3. Replace Ignition Coil (if needed)

• If the ignition coil was found faulty during diagnostics:
  • Remove the faulty ignition coil as described above.
  • Install a new ignition coil in cylinder 2.
  • Ensure it is seated correctly and reconnect the electrical connector.

4. Check Fuel Injector (if needed)

• If the fuel injector is faulty:
  • Disconnect the fuel injector connector.
  • Remove the fuel injector from cylinder 2.
  • Install a new fuel injector ensuring it is properly seated and connected.

5. Reassemble and Test

• Reconnect the battery and ensure all connections are secure.
• Start the engine and allow it to idle for a few minutes.
• Check for any new codes using the OBD-II scanner and monitor engine performance.