how to diagnose P0301 code on my BMW 3 Series E90/E91 (2005-2012)?

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery to ensure safety during repairs.

2. Inspect and Replace Spark Plug

• Tools Required: Socket set, torque wrench
• Remove the engine cover if necessary.
• Use a socket to remove the spark plug from cylinder 1.
• Inspect the spark plug for signs of wear, oil deposits, or carbon buildup.
• If damaged, replace with a new spark plug, ensuring it meets OEM specifications.
• Torque the spark plug to the manufacturer’s recommended value (typically around 18-22 lb-ft).

3. Test and Replace Ignition Coil

• Tools Required: Multimeter, socket set
• Disconnect the electrical connector from the ignition coil for cylinder 1.
• Use a multimeter to test the coil's primary and secondary resistance values.
• If the resistance values are outside the specifications, replace the ignition coil with a new one.
• Reconnect the ignition coil and ensure it is secured properly.

4. Inspect and Clean Fuel Injector

• Tools Required: Injector cleaning kit
• Remove the fuel injector from cylinder 1 by disconnecting the fuel rail.
• Check for clogs or leaks in the fuel injector.
• If necessary, use an injector cleaning kit to clean the injector or replace it if cleaning is ineffective.
• Reinstall the fuel injector and ensure all connections are secure.

5. Perform Compression Test

• Tools Required: Compression tester
• Remove the spark plug from cylinder 1.
• Insert the compression tester into the spark plug hole.
• Crank the engine a few times and record the compression reading.
• Compare the reading to the manufacturer’s specifications. If it’s low, further investigation of engine internals may be required.