how to troubleshoot P0303 misfire code in my BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, compression tester, spark plug socket, ratchet, torque wrench, noid light (if testing injectors).
• Disconnect the negative battery terminal to ensure safety while working on electrical components.

2. Replace Spark Plug (if faulty)

• Remove the ignition coil for cylinder 3:
  1. Unplug the electrical connector from the ignition coil.
  2. Remove the retaining bolt and gently pull the coil out.
• Inspect the spark plug:
  1. Use a spark plug socket to remove the spark plug.
  2. Check for signs of fouling or damage.
• Install a new spark plug:
  1. Gap the new spark plug to the manufacturer’s specifications (usually around 0.032-0.036 inches).
  2. Insert the new spark plug and torque to the manufacturer’s specifications (typically 15-20 lb-ft).
  3. Reinstall the ignition coil and reconnect the electrical connector.

3. Replace Ignition Coil (if faulty)

• If the ignition coil is defective:
  1. Remove the ignition coil as described above.
  2. Install a new ignition coil, ensuring it is seated properly.
  3. Reconnect the electrical connector.

4. Check Fuel Injector (if faulty)

• If the fuel injector is suspected to be faulty:
  1. Disconnect the fuel injector connector for cylinder 3.
  2. Connect a noid light to check for signal or use a multimeter to measure resistance.
  3. If the injector is not functioning, replace it with a new one.
  4. Reconnect the fuel injector connector after replacement.

5. Reassemble and Final Checks

• Reconnect the negative battery terminal.
• Clear the error codes using the OBD-II scanner.
• Start the engine and monitor for smooth operation.