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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shocks.

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 1:
  • Unscrew the mounting bolts using a socket set.
  • Carefully lift the coil out.
• Remove the spark plug:
  • Use a spark plug socket to unscrew the old spark plug.
  • Inspect the spark plug for wear, carbon buildup, or damage.
• Install a new spark plug:
  • Ensure the new spark plug is gapped correctly (usually 0.032-0.036 inches for BMW).
  • Torque the spark plug to the manufacturer’s specification (typically around 15 ft-lbs).
• Reinstall the ignition coil:
  • Ensure the coil is seated properly and secure it with bolts.

3. Inspect and Replace Ignition Coil (if necessary)

• If the ignition coil appears damaged or if replacing the spark plug doesn’t resolve the issue:
  • Replace the ignition coil with a new one.
  • Reconnect the electrical connector and secure it.

4. Check Fuel Injector

• If misfire persists, inspect the fuel injector for cylinder 1:
  • Remove the fuel rail if necessary to access the injector.
  • Test the injector for proper operation (using a multimeter or injector test tool).
  • Replace the injector if it is faulty.

5. Compression Test

• If the issue remains unresolved, perform a compression test:
  • Remove the spark plug and coil again.
  • Insert the compression gauge into the spark plug hole.
  • Crank the engine and record the compression reading.
  • Compare with manufacturer specifications (typically around 150-200 PSI).
  • If compression is low, further diagnosis for internal engine issues may be required.