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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.

Tools Required:

• OBD-II scanner
• Socket set
• Torque wrench
• Compression tester
• Multimeter
• Noid light
• Screwdrivers
• Safety goggles and gloves

2. Inspect and Replace Spark Plug

• Step 1: Remove the engine cover if applicable.
• Step 2: Locate and remove the ignition coil from cylinder 1 by unscrewing the bolts and disconnecting the electrical connector.
• Step 3: Remove the spark plug from cylinder 1 using a spark plug socket and ratchet.
• Step 4: Inspect the spark plug for wear; replace it with a new spark plug if necessary.
• Step 5: Reinstall the spark plug, tightening to the manufacturer’s specified torque (usually around 18 lb-ft for BMW).
• Step 6: Reinstall the ignition coil and reconnect the electrical connector.

3. Test and Replace Ignition Coil

• Step 1: If the spark plug is fine, test the ignition coil using a multimeter for proper resistance.
• Step 2: If the coil is faulty, replace it with a new ignition coil specific to your vehicle model.
• Step 3: Reconnect all components and ensure secure fittings.

4. Inspect and Replace Fuel Injector

• Step 1: If misfire persists, check the fuel injector for cylinder 1 using a noid light to ensure it’s receiving the proper signal.
• Step 2: If the injector is faulty, remove it from the rail by releasing the clips and disconnecting the electrical connector.
• Step 3: Install a new fuel injector, ensuring it is properly seated and connected.

5. Compression Test

• Step 1: If the misfire continues, perform a compression test on cylinder 1.
• Step 2: Remove the spark plug and insert the compression tester.
• Step 3: Crank the engine and note the compression reading; it should meet manufacturer specifications (typically around 140-200 psi).
• Step 4: If low compression is found, further investigation of the engine internals is necessary.