my BMW 3 Series F30/F31 (2012-2019) won't start when it's cold

Solution

1. Preparation

• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative terminal of the battery to prevent electrical shorts.

2. Battery Check

• Sub-steps:
  • Remove the battery terminals (negative first, then positive).
  • Use a multimeter to test the battery voltage; replace the battery if below 12.4 volts.
  • Clean the battery terminals and cable connectors to ensure a good connection.

3. Fuel System Inspection

• Sub-steps:
  • Locate the fuel pump relay and check for continuity using a multimeter.
  • If necessary, replace the fuel pump relay.
  • Connect a fuel pressure gauge to the fuel rail and turn the ignition to the "ON" position (do not crank). Verify that the fuel pressure is within specifications (typically 50-60 psi).
  • Replace the fuel filter if it appears clogged or if the pressure is low.

4. Ignition System Repair

• Sub-steps:
  • Remove the ignition coils and inspect for cracks or carbon tracking.
  • Test each ignition coil with an ohmmeter; replace any that do not meet specifications.
  • Remove and inspect the spark plugs for wear; replace if the electrodes are worn or fouled.

5. Engine Coolant Temperature Sensor Replacement

• Sub-steps:
  • Locate the engine coolant temperature sensor (usually near the thermostat housing).
  • Disconnect the electrical connector and remove the sensor using a socket.
  • Install the new sensor with the appropriate torque (typically around 15 Nm).
  • Reconnect the electrical connector.

6. Reassembly

• Reconnect the battery terminals (positive first, then negative).
• Start the engine and allow it to reach operating temperature to confirm proper functionality.