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

Solution

1. Preparation

• Gather tools and parts necessary for the repair.
• Disconnect the battery, ensuring safety while working on electrical components.
• Allow the engine to cool completely before starting work.

2. Inspect and Replace Spark Plug

• Tools Required: Spark plug socket, torque wrench, ratchet.
• Sub-steps:
  1. Remove the engine cover to access the spark plugs.
  2. Use the spark plug socket to carefully unscrew and remove the spark plug from Cylinder 1.
  3. Inspect the spark plug for signs of wear or fouling. If damaged, replace it with an OEM or equivalent spark plug.
  4. Torque the new spark plug to the manufacturer’s specifications (typically around 18-22 ft-lbs).
  5. Reinstall the engine cover.

3. Inspect and Replace Ignition Coil

• Tools Required: Ratchet, socket set.
• Sub-steps:
  1. Disconnect the electrical connector from the ignition coil for Cylinder 1.
  2. Remove the bolts securing the ignition coil and pull it out.
  3. Inspect the coil for cracks or damage. Replace it if necessary with a new ignition coil.
  4. Reinstall the new ignition coil and reconnect the electrical connector.

4. Check and Replace Fuel Injector

• Tools Required: Fuel injector removal tool, ratchet, and socket set.
• Sub-steps:
  1. Relieve fuel system pressure by removing the fuel pump fuse and starting the engine until it stalls.
  2. Disconnect the fuel line and the electrical connector from the fuel injector for Cylinder 1.
  3. Remove the retaining clips and pull the fuel injector out.
  4. Inspect the injector for clogs or leaks. Replace if necessary with an OEM fuel injector.
  5. Reinstall the fuel injector and reconnect the fuel line and electrical connector.

5. Perform Compression Test

• Tools Required: Compression tester.
• Sub-steps:
  1. Remove the spark plug from Cylinder 1.
  2. Insert the compression tester into the spark plug hole and crank the engine.
  3. Note the compression reading. Compare with manufacturer specifications (typically around 120-150 psi).
  4. If compression is low, further investigation into potential engine issues (valve problems, head gasket failure) is necessary.