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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent any electrical shorts.

2. Replace Ignition Coil and Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket, dielectric grease.
• Remove the engine cover (if applicable) to access the ignition coil.
• Disconnect the electrical connector from the ignition coil.
• Remove the ignition coil by unscrewing the retaining bolt and pulling it out.
• Remove the spark plug using a spark plug socket. Inspect it for wear or damage; replace if necessary.
• Install the new spark plug, tightening it to manufacturer specifications (typically 15-20 lb-ft).
• Apply dielectric grease to the ignition coil connector and reinstall the ignition coil, securing it with the bolt.

3. Test Fuel Injector

• Tools Required: Noid light or multimeter.
• Disconnect the fuel injector connector from cylinder 1.
• Connect a noid light to the injector connector to check for signal; if no signal, further diagnose the wiring.
• If the signal is present, perform a resistance test using a multimeter. Replace the fuel injector if it is out of specification.

4. Compression Test

• Tools Required: Compression tester.
• Remove all spark plugs to facilitate easier cranking.
• Insert the compression tester into the spark plug hole of cylinder 1.
• Crank the engine for a few seconds and record the compression reading. Compare it to specifications; replace any damaged components if compression is low.