how to fix P0300 code in my BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools and parts required for repair.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to avoid electrical shocks.

2. Inspect and Replace Spark Plugs

• Remove the ignition coil covers (if applicable) using a socket set.
• Disconnect the electrical connectors from the ignition coils.
• Remove the ignition coils using a socket wrench.
• Remove old spark plugs with a spark plug socket.
• Inspect spark plugs for wear; replace with OEM or equivalent if damaged.
• Install new spark plugs with the correct gap (typically 0.030 inches for BMW).
• Reinstall ignition coils, ensuring proper seating and reconnect electrical connectors.

3. Inspect and Replace Ignition Coils

• If misfires persist, test each ignition coil with a multimeter for resistance.
• Replace any faulty ignition coils with OEM parts.
• Reassemble components and ensure all connectors are secure.

4. Fuel System Check

• Connect a fuel pressure gauge to the fuel rail.
• Turn the ignition to the "on" position (do not start) and check fuel pressure.
• If pressure is below specifications (usually around 50-60 psi), check the fuel pump and filter for issues.
• Replace the fuel filter and, if necessary, the fuel pump.

5. Check for Vacuum Leaks

• Inspect all vacuum hoses and intake manifold gaskets visually and by touch for tears or disconnections.
• Replace any damaged hoses or gaskets.

6. Compression Test

• Perform a compression test on all cylinders.
• Record values; if compression is below specifications (typically 120 psi), further investigation of internal engine components may be needed.