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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety while working on electrical components.
• Allow the engine to cool before starting work.

2. Replace Spark Plug

• Tools Required: Spark plug socket, ratchet, torque wrench.
• Remove the ignition coil from cylinder 1 by unscrewing the retaining bolt and lifting it out.
• Use the spark plug socket to remove the spark plug from cylinder 1.
• Inspect the spark plug for wear; replace it if it shows signs of fouling or damage.
• Install the new spark plug, ensuring it is torqued to the manufacturer's specification (typically around 22 Nm).
• Reinstall the ignition coil, securing it with the retaining bolt.

3. Replace Ignition Coil (if necessary)

• Tools Required: Ratchet, socket set.
• If the ignition coil shows signs of damage, remove it from cylinder 1 as described above.
• Install the new ignition coil by reversing the removal process, ensuring it clicks into place and is secured properly.

4. Test Fuel Injector

• Tools Required: Fuel injector tester (or multimeter).
• Disconnect the electrical connector from the fuel injector for cylinder 1.
• Use the fuel injector tester to check for proper operation. If it does not function, replace the fuel injector.
• Reconnect the fuel injector once testing is complete.

5. Compression Test (if necessary)

• Tools Required: Compression tester.
• Remove the spark plug from cylinder 1.
• Insert the compression tester into the spark plug hole and crank the engine.
• Record the compression reading. If it is significantly lower than the manufacturer's specification, there may be internal engine issues requiring further investigation.