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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before proceeding.

2. Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket.
• Remove the engine cover (if applicable) to access the spark plug.
• Using the spark plug socket, remove the spark plug from cylinder 1.
• Inspect the old spark plug and replace it with a new one, ensuring it is the correct type (OEM recommended).
• Torque the new spark plug to the manufacturer's specifications (typically around 18-22 lb-ft).

3. Inspect and Replace Ignition Coil

• Tools Required: Socket set, multimeter.
• Disconnect the electrical connector from the ignition coil for cylinder 1.
• Remove the ignition coil by unscrewing it from the cylinder head.
• Test the ignition coil using a multimeter to ensure it has the correct resistance (typically 0.5 to 1.5 ohms for primary).
• If faulty, replace with a new ignition coil and reconnect the electrical connector.

4. Check Fuel Injector

• Tools Required: Noid light or fuel pressure gauge.
• Disconnect the fuel injector connector for cylinder 1.
• Use a noid light to check if the injector is receiving the correct signal (the light should flash while cranking).
• If the injector is not functioning, remove it and replace with a new one, ensuring proper seating and connection.

5. Verify Compression

• Tools Required: Compression tester.
• Remove the spark plug from cylinder 1.
• Insert the compression tester into the spark plug hole and crank the engine.
• Check the compression reading; compare it with the manufacturer’s specifications (usually around 130-200 psi).
• If compression is low, further diagnosis may be needed for potential valve or head gasket issues.