how to fix P0300 misfire code in BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety while working on the electrical components.

Tools Required:

• OBD-II scanner
• Socket set (including spark plug socket)
• Multimeter
• Fuel pressure gauge
• Torque wrench

2. Replace Spark Plugs

1. Remove the engine cover if applicable.
2. Use a socket wrench to remove the spark plugs:
   • Ensure to inspect each plug for wear; replace all if any are faulty.
   • Torque new spark plugs to the manufacturer’s specifications (typically around 20 Nm).
3. Reinstall the engine cover.

3. Inspect and Replace Ignition Coils

1. Locate the ignition coils on the engine; remove the electrical connectors carefully.
2. Unbolt the coils using a socket wrench and remove them from the engine.
3. Install new ignition coils, ensuring they are seated properly and reconnect electrical connectors.
4. Torque bolts to manufacturer specifications.

4. Test and Replace Fuel Injectors (if necessary)

1. Disconnect the fuel pump relay and start the engine until it stalls to relieve fuel pressure.
2. Remove the fuel rail assembly, taking care to note the orientation of injectors.
3. Check each injector for clogs or leaks; replace any faulty injectors.
4. Reassemble the fuel rail with new O-rings.

5. Check for Vacuum Leaks

1. Visually inspect all vacuum lines and intake manifold gaskets for cracks or disconnections.
2. Use a smoke machine to identify any leaks, repairing as necessary.

6. Verify Fuel Pressure

1. Attach a fuel pressure gauge to the fuel rail.
2. Turn the ignition on (do not start the engine) and check the pressure; it should be within specifications.
3. If low, check the fuel pump and filter for blockage or failure.