how to fix P0301 misfire code in BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the vehicle battery to ensure safety while working on electrical components.

2. Replace Ignition Coil

• Tools Required: Socket set, torque wrench, dielectric grease
• Remove the engine cover if necessary.
• Disconnect the electrical connector from the ignition coil.
• Remove the bolt securing the ignition coil using a socket.
• Pull the ignition coil out from the cylinder head.
• Install the new ignition coil by reversing the removal steps.
• Apply dielectric grease to the electrical connector before reconnecting.

3. Replace Spark Plug

• Tools Required: Spark plug socket, torque wrench, gap gauge
• Remove the ignition coil again if it was replaced previously to access the spark plug.
• Use a spark plug socket to unscrew the old spark plug from cylinder 1.
• Inspect the old spark plug for wear or carbon buildup.
• Set the gap on the new spark plug to manufacturer specifications (typically around 0.030-0.040 inches).
• Install the new spark plug by hand to avoid cross-threading, then torque it to manufacturer specifications (usually around 18 ft-lbs).
• Reinstall the ignition coil.

4. Test Injector Functionality

• Tools Required: Noid light or multimeter
• Disconnect the fuel injector connector from cylinder 1.
• Connect the noid light to the injector connector to check for pulse signals while the engine is cranking.
• If the noid light does not flash, check the wiring and the engine control module.
• If necessary, replace the fuel injector for cylinder 1.

5. Reassemble and Clear Codes

• Reconnect any components removed during the process, including the battery and engine cover.
• Clear the P0301 code using the OBD-II scanner.
• Start the vehicle and allow it to idle.