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 ensure safety while working.

2. Addressing Error Codes

• Sub-step 1: Note down the error codes retrieved from the OBD-II scanner.
• Sub-step 2: Research the specific codes to understand the underlying issue (e.g., P0300 for random misfire).

3. Replace Faulty Components

• Sub-step 1: If spark plugs are worn, remove the ignition coils using a socket set and replace the spark plugs with the manufacturer's recommended type.
• Sub-step 2: For faulty ignition coils, remove the old coils and install new ones, ensuring they are seated properly.

4. Repairing Vacuum Leaks

• Sub-step 1: Locate any vacuum hoses and inspect for cracks or disconnections.
• Sub-step 2: Replace any damaged hoses using appropriate sizes and types, securing with clamps where necessary.

5. Inspecting and Cleaning MAF Sensor

• Sub-step 1: Disconnect the MAF sensor connector and remove the sensor from its housing.
• Sub-step 2: Clean the MAF sensor with a dedicated cleaner and allow it to dry before reinstallation.

6. Testing Fuel Pressure

• Sub-step 1: Connect a fuel pressure gauge to the fuel rail and turn the ignition to the "on" position without starting the engine.
• Sub-step 2: Observe the pressure reading; it should match manufacturer specifications. Replace the fuel pump or filter if pressure is low.