what does it mean when my BMW 3 Series G20/G21 (2019-2024) check engine light comes on

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is off.
• Disconnect the battery negative terminal to prevent electrical shorts.

2. Scan and Interpret Codes

• Use an OBD-II scanner to read stored diagnostic trouble codes (DTCs).
• Record the codes for further analysis and clear them to see if they return.

3. Address Detected Issues

• For P0420 (Catalytic Converter Efficiency Below Threshold):
  • Inspect catalytic converter for damage or blockage.
  • Replace O2 sensors if indicated by codes or if they are malfunctioning.
• For P0171/P0174 (System Too Lean):
  • Check for vacuum leaks using a smoke machine.
  • Inspect and clean the mass air flow (MAF) sensor.
  • Replace faulty fuel injectors if necessary.
• For P0300 (Random Misfire Detected):
  • Inspect spark plugs and ignition coils; replace if worn or faulty.
  • Check fuel delivery system for pressure and leaks.

4. Reassemble and Test

• Once repairs are completed, reconnect the battery.
• Start the engine and allow it to reach operating temperature.
• Monitor engine performance and check for any reoccurring codes.