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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the engine is cool and disconnect the negative battery terminal.
• Tools Required: OBD-II scanner, spark plug socket, compression tester, multimeter, torque wrench.

2. Replace Spark Plug

• Remove the ignition coil from cylinder 1.
• Use a spark plug socket to remove the old spark plug.
• Install a new spark plug, ensuring it is gapped correctly (refer to manufacturer specifications).
• Torque the spark plug to the specified value (typically around 15 lb-ft for BMW).

3. Inspect and Replace Ignition Coil

• If the ignition coil appears faulty (e.g., cracked casing, corrosion), replace it with a new one.
• To replace, remove the bolts securing the coil, lift it out, and install the new coil in reverse order.
• Ensure the connector is secure and check for proper fit.

4. Test Compression (if necessary)

• Insert the compression tester into the spark plug hole for cylinder 1.
• Crank the engine and record the compression reading.
• Compare to manufacturer specifications (typically around 140-200 psi). If low, further investigation into internal engine components may be necessary.

5. Inspect and Clean Fuel Injector

• If the fuel injector is suspected to be clogged, remove it from the rail.
• Clean the injector using a specialized cleaner or replace it if necessary.
• Reinstall the injector ensuring it clicks into place and reconnect any electrical connectors.