how to diagnose the P0301 code in my BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to avoid electrical shorts.
• Ensure engine is cool to prevent burns.

2. Replace Spark Plug

• Remove the engine cover (if applicable) using a socket set.
• Locate spark plug for cylinder 1 (refer to the engine layout).
• Use a spark plug socket and ratchet to remove the old spark plug.
• Inspect the old spark plug for signs of damage (e.g., carbon buildup, wear).
• Install a new spark plug with the correct gap (typically 0.024-0.028 inches for BMW).
• Torque the spark plug to the manufacturer’s specifications (usually around 18-22 lb-ft).

3. Check and Replace Ignition Coil

• Remove the ignition coil connector by pressing the release tab and pulling it out.
• Remove the ignition coil bolt using a socket wrench.
• Carefully pull out the ignition coil from the cylinder head.
• Inspect the ignition coil for cracks or signs of arcing.
• If faulty, replace with a new ignition coil that is compatible with the BMW G20/G21.
• Reinstall the ignition coil and reconnect the electrical connector.

4. Perform Compression Test

• Remove the spark plug for cylinder 1.
• Install the compression gauge into the spark plug hole.
• Crank the engine a few times to get a reading.
• Compare the reading to the manufacturer specifications (generally, should be around 130-150 psi).
• If compression is low, further inspection of piston rings or valves may be necessary.

5. Inspect Fuel Injector

• Disconnect the fuel injector connector for cylinder 1.
• Remove the fuel rail (if necessary) to access the injector.
• Check for clogs or leaks in the injector.
• If necessary, replace the fuel injector with a new one.
• Reinstall the fuel rail and reconnect all connectors.

6. Check for Vacuum Leaks

• Inspect the intake manifold and vacuum hoses for cracks or leaks.
• Use a smoke machine or carb cleaner spray around the intake area while the engine is running to identify leaks.
• Repair or replace damaged hoses or gaskets as needed.