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

Solution

1. Preparation

• Gather tools and materials: OBD-II scanner, compression gauge, spark plug socket, torque wrench, fuel injector cleaner.
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Replace Ignition Components

• Ignition Coil:

  1. Disconnect the negative battery terminal.
  2. Remove the engine cover if applicable.
  3. Disconnect the wiring harness from the ignition coil on cylinder 1.
  4. Remove the ignition coil using a socket and ratchet.
  5. Install the new ignition coil and reconnect the wiring harness.

• Spark Plug:

  1. Use the spark plug socket to remove the spark plug from cylinder 1.
  2. Inspect the old spark plug for wear or fouling.
  3. Gap the new spark plug according to specifications (typically between 0.028-0.032 inches).
  4. Install the new spark plug and torque to manufacturer specifications (usually around 18-22 lb-ft).

3. Clean or Replace Fuel Injector

• If the injector is clogged:
  1. Disconnect the fuel line from the injector rail.
  2. Remove the fuel injector using a suitable tool.
  3. Clean the injector using an ultrasonic cleaner or replace it with a new injector.
  4. Reinstall the injector and reconnect the fuel line.

4. Perform Compression Test

1. Remove the spark plug from cylinder 1.
2. Insert the compression gauge into the spark plug hole.
3. Crank the engine several times and note the compression reading.
4. If compression is below manufacturer specifications (usually around 150-200 psi), further investigation into engine internals may be needed.