how to fix P0300 misfire code on BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface, and the engine is cool.
• Disconnect the negative battery terminal.

2. Inspect and Replace Spark Plugs

• Tools Required: Socket set, torque wrench, spark plug socket, dielectric grease.
• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Disconnect ignition coils from the spark plugs.
  3. Remove the spark plugs using a spark plug socket.
  4. Inspect the spark plugs for wear or fouling and replace if necessary.
  5. Apply dielectric grease to the ignition coil boots.
  6. Reinstall new or cleaned spark plugs and torque them to manufacturer specifications (typically 22 lb-ft for BMW).

3. Inspect and Replace Ignition Coils

• Tools Required: Socket set, dielectric grease.
• Sub-steps:
  1. Remove the ignition coils from their respective spark plugs.
  2. Inspect each ignition coil for cracks or signs of arcing.
  3. Replace any faulty ignition coils with new ones.
  4. Reconnect ignition coils and ensure proper seating.

4. Check and Repair Vacuum Leaks

• Tools Required: Smoke machine or carburetor cleaner.
• Sub-steps:
  1. Use a smoke machine to inject smoke into the intake system to identify leaks.
  2. Alternatively, spray carburetor cleaner around the intake manifold and vacuum hoses; listen for RPM changes.
  3. Repair or replace any damaged hoses or gaskets found during inspection.

5. Test Fuel Pressure

• Tools Required: Fuel pressure gauge.
• Sub-steps:
  1. Locate the fuel rail and connect the fuel pressure gauge.
  2. Turn the ignition to the "ON" position without starting the engine to check the pressure.
  3. Compare the reading with manufacturer specifications (typically 50-60 psi for BMW).
  4. If pressure is low, inspect the fuel pump and fuel filter for issues.