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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical short circuits.
• Allow the engine to cool down before starting work.

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 1:
  • Use a socket set to remove the bolts securing the ignition coil.
  • Gently pull the ignition coil out.
• Remove the spark plug:
  • Use a spark plug socket to unscrew the spark plug from cylinder 1.
• Inspect the spark plug for wear or fouling; if damaged, replace it with a new one:
  • Recommended gap: 0.032 inches (0.8 mm).
• Reinstall the new spark plug and ignition coil in the reverse order.

3. Test and Replace Ignition Coil

• If the spark plug is in good condition, test the ignition coil:
  • Use a multimeter to check the primary and secondary resistance of the coil.
• If the ignition coil is faulty, replace it with a new one:
  • Ensure the coil is properly seated and secured with bolts.

4. Inspect and Replace Fuel Injector

• If the ignition system is functioning, test the fuel injector:
  • Remove the electrical connector and use a multimeter to check for continuity.
• If the injector is defective, replace it with a new one:
  • Ensure to use the correct part number based on the vehicle specifications.

5. Perform Compression Test

• If misfire persists, perform a compression test on cylinder 1:
  • Remove the spark plug and attach the compression gauge to the spark plug hole.
  • Crank the engine and record the compression reading; it should be within the manufacturer's specifications (typically around 140-200 psi).
• If compression is low, further investigation is needed for potential internal engine issues.