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

Solution

1. Preparation

• Gather tools and parts needed.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool down.

2. Inspect and Replace Spark Plug

• Tools Required: Spark plug socket, torque wrench
• Remove the ignition coil and spark plug from cylinder 1:
  1. Unplug the ignition coil connector.
  2. Remove the bolt securing the ignition coil and gently pull out the coil.
  3. Use a spark plug socket to remove the spark plug.
• Inspect the spark plug for wear or damage:
  • Replace with a new spark plug if necessary. Torque to the manufacturer’s specification (usually around 22 ft-lbs).

3. Check and Replace Ignition Coil

• Tools Required: Socket set, torque wrench
• If the spark plug is fine, check the ignition coil:
  1. Connect a multimeter to the ignition coil to test for primary and secondary resistance according to the service manual specifications.
  2. If the ignition coil is faulty, replace it with a new one. Torque the ignition coil retaining bolt to manufacturer specifications (typically around 10-15 ft-lbs).

4. Compression Test

• Tools Required: Compression tester
• If misfire persists, conduct a compression test:
  1. Remove the spark plug from cylinder 1.
  2. Insert the compression tester into the spark plug hole.
  3. Crank the engine and record the compression reading. Compare it to manufacturer specifications.
• If compression is low, further engine diagnostics may be required (e.g., valve issues, piston rings).

5. Inspect and Clean Fuel Injector

• Tools Required: Fuel injector cleaner, basic hand tools
• If the ignition coil and spark plug are good, check the fuel injector:
  1. Remove the fuel injector from cylinder 1 using appropriate tools.
  2. Inspect for clogs or leaks.
  3. Clean or replace the injector as necessary.

6. Check for Vacuum Leaks

• Tools Required: Smoke machine or carburetor cleaner
• Inspect for vacuum leaks:
  1. Use a smoke machine to find leaks around the intake manifold and hoses.
  2. If a leak is found, replace or repair the affected component.