why does my BMW 3 Series E90/E91 (2005-2012) check engine light keep coming on

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent any electrical shorts.
• Allow the engine to cool before starting work.

2. Inspect and Replace Gas Cap

• Remove the gas cap and inspect for cracks or damage.
• If damaged, replace it with a new gas cap.
• Reinstall the gas cap securely to ensure proper sealing.

3. Change Engine Oil and Filter

• Drain the engine oil using a socket set and oil catch pan.
• Replace the oil filter with a new one, ensuring proper orientation.
• Refill the engine with the correct grade of oil as specified in the owner’s manual.

4. Replace Air Filter

• Open the air filter housing by unclipping or unscrewing.
• Remove the old air filter and clean the housing.
• Install the new air filter, ensuring it fits snugly.

5. Replace Spark Plugs and Ignition Coils (if needed)

• Remove ignition coil covers using a socket set.
• Disconnect the electrical connectors from the ignition coils.
• Remove the spark plugs using a spark plug socket.
• Install new spark plugs, tightening to manufacturer specifications (typically 15-20 Nm).
• Reinstall ignition coils and reconnect the electrical connectors.

6. Test Fuel Pressure

• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition to the “on” position (do not start the engine) and check pressure readings against manufacturer specifications.
• If pressure is low, inspect the fuel pump and filter for issues.