how to fix P0303 code on BMW X3 F25 (2011-2018)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the engine is cool and disconnect the negative battery terminal.

Tools Required:

• OBD-II scanner
• Spark plug socket
• Torque wrench
• Compression tester
• Noid light or multimeter
• Basic hand tools (sockets, wrenches)

2. Inspect and Replace Spark Plug

• Remove the ignition coil from cylinder 3 by unscrewing the retaining bolts.
• Pull out the spark plug using the spark plug socket.
• Inspect the spark plug for fouling, wear, or damage; replace if necessary.
• Ensure the gap is set to manufacturer specifications (typically around 0.028-0.032 inches).

3. Inspect and Replace Ignition Coil

• If the spark plug is fine, test the ignition coil using a multimeter. Measure resistance according to manufacturer specifications.
• If faulty, replace the ignition coil with a new one.
• Reinstall the ignition coil and ensure it is securely fastened.

4. Check Fuel Injector

• Disconnect the electrical connector from the fuel injector for cylinder 3.
• Use a noid light or multimeter to check for proper signal and voltage.
• If the injector is malfunctioning, replace it with a new one.
• Reconnect the injector and ensure it is properly seated in the fuel rail.

5. Perform Compression Test

• Remove the spark plug from cylinder 3.
• Insert the compression tester into the spark plug hole.
• Crank the engine and record the compression reading; it should be within the manufacturer's specifications (typically around 150-200 psi).
• If compression is low, further investigation into valve, piston, or gasket issues may be required.

6. Reassemble and Test

• Reinstall the spark plug and ignition coil if all components are functioning correctly.
• Reconnect the negative battery terminal.
• Clear the DTCs with the OBD-II scanner and start the engine.
• Allow the engine to reach operating temperature and monitor for any returning codes.