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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool down.

2. Inspect and Replace Spark Plug

• Tools Required: Socket set, torque wrench, spark plug socket.
• Remove the ignition coil by unscrewing the retaining bolt and gently pulling it out.
• Remove the spark plug using a spark plug socket. Inspect the spark plug for wear, damage, or fouling.
• Replace with a new spark plug, ensuring it is gapped correctly to manufacturer specifications (refer to the owner’s manual for specific gap size).
• Torque the spark plug to the recommended specification (typically around 15 lb-ft).

3. Inspect and Replace Ignition Coil

• If the spark plug is in good condition, inspect the ignition coil for any signs of damage or corrosion.
• If necessary, replace the ignition coil with a new one.
• Reinstall the ignition coil and secure it with the retaining bolt.

4. Inspect Fuel Injector

• Tools Required: Fuel injector testing kit (if needed).
• Remove the fuel injector connector and inspect for damage.
• If available, use a fuel injector testing kit to verify that the injector is functioning properly. Replace if it is faulty.

5. Compression Test

• Tools Required: Compression gauge.
• Remove the spark plug from cylinder 1.
• Insert the compression gauge into the spark plug hole and crank the engine to obtain a compression reading.
• Compare the reading to manufacturer specifications; if low, further investigation into engine internals may be necessary.