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

Solution

1. Preparation

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

2. Inspect and Replace Spark Plug

• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Disconnect the ignition coil connector from cylinder 1.
  3. Remove the ignition coil by unscrewing it from the cylinder head.
  4. Inspect the spark plug; if worn, use a spark plug socket to remove it.
  5. Install a new spark plug (ensure correct gap according to specifications).
  6. Reinstall the ignition coil and connect the connector.

3. Test and Replace Ignition Coil (if necessary)

• Sub-steps:
  1. If the spark plug is in good condition, test the ignition coil using a multimeter for primary and secondary resistance.
  2. If out of specification, replace the ignition coil with a new one.
  3. Reconnect the ignition coil and ensure it is seated properly.

4. Inspect and Replace Fuel Injector (if necessary)

• Sub-steps:
  1. Disconnect the fuel injector connector for cylinder 1.
  2. Remove the fuel rail if necessary (ensure to relieve fuel pressure first).
  3. Inspect the injector for clogs or damage.
  4. If faulty, replace the fuel injector with a new one.
  5. Reinstall the fuel rail and reconnect the injector connector.

5. Reassemble and Test

• Sub-steps:
  1. Reinstall any components that were removed for access.
  2. Reconnect the negative battery terminal.
  3. Start the engine and let it reach operating temperature.