how to diagnose P0171 code in BMW 3 Series F30/F31 (2012-2019)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.

2. Inspect Air Intake System

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Apply a smoke test if necessary to identify any hidden leaks.
• Tools Required: Smoke machine (optional)

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor electrical connector.
  2. Remove the MAF sensor from the intake.
  3. Clean the MAF sensor using MAF cleaner. Allow it to dry before reinstalling.
  4. If cleaning does not resolve the issue, replace the MAF sensor with a new one.
• Tools Required: Torx screwdriver, MAF cleaner

4. Check Fuel Pressure

• Sub-steps:
  1. Locate the fuel pressure test port on the fuel rail.
  2. Attach the fuel pressure gauge to the test port.
  3. Turn the ignition to the "ON" position (do not start the engine) to check pressure.
  4. Compare the reading to manufacturer specifications (typically 50-60 psi).
  5. If pressure is low, check the fuel pump and fuel filter.
• Tools Required: Fuel pressure gauge

5. Inspect Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail cover to access the fuel injectors.
  2. Check for any visible fuel leaks around the injectors.
  3. Use a multimeter to check the resistance of each injector. Compare readings to specifications.
  4. If any injector is faulty, replace it.
• Tools Required: Multimeter, socket set

6. Verify Coolant Temperature Sensor

• Sub-steps:
  1. Locate the coolant temperature sensor connected to the engine.
  2. Disconnect the sensor and measure its resistance using a multimeter.
  3. Compare the resistance reading at various temperatures to manufacturer specifications.
  4. Replace the sensor if it is out of specification.
• Tools Required: Multimeter, socket set