why does my BMW 3 Series E90/E91 (2005-2012) engine light stay on after resetting

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool before beginning any repairs.

2. Address Identified Trouble Codes

• Based on the OBD-II scan results, follow the specific repair procedures for the identified codes.
  • Example: If code P0420 (catalytic converter efficiency below threshold):
    • Inspect and replace the oxygen sensors if faulty.
    • Check for exhaust leaks before the catalytic converter.
    • Replace the catalytic converter if it is confirmed to be faulty.

3. Inspect and Replace Ignition Components

• Remove the engine cover to access ignition coils and spark plugs.
• Tools Required: Socket set, torque wrench.
• Sub-steps:
  1. Remove ignition coils and inspect for cracks or damage.
  2. Replace faulty coils with new ones (ensure proper torque specifications during reinstallation).
  3. Remove spark plugs and inspect for wear; replace if necessary.
  4. Reinstall the ignition coils and engine cover.

4. Clean or Replace Air Intake Components

• Check the air filter and intake hoses:
  1. Remove the air intake duct and inspect the air filter; replace if dirty.
  2. Check for cracks or loose connections in intake hoses and replace as needed.
  3. Reassemble the air intake duct securely.

5. Fuel System Inspection

• Check fuel injectors and fuel pressure:
  1. Inspect fuel lines for leaks.
  2. Test fuel pressure with a fuel pressure gauge; replace the fuel pump if pressure is low.
  3. Clean fuel injectors using a fuel injector cleaning kit if they are found to be clogged.