how to fix the P0171 code on my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery to ensure safety while working on the vehicle.
• Allow the engine to cool down if it has been running.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum lines connected to the intake manifold.
  • Use a smoke machine or carburetor cleaner to identify any leaks.
  • Replace any damaged hoses or connections as necessary.

3. Clean or Replace MAF Sensor

• Sub-steps:
  • Locate the MAF sensor in the air intake duct.
  • Disconnect the electrical connector and remove the MAF sensor.
  • Clean the sensor with MAF cleaner spray (do not use other cleaners).
  • Reinstall the MAF sensor, ensuring the electrical connector is properly attached.
  • If the sensor is faulty, replace it with a new one.

4. Check and Repair Fuel System

• Sub-steps:
  • Connect a fuel pressure gauge to the fuel rail.
  • Turn the ignition to the ON position (do not start) and check the fuel pressure.
  • If the pressure is low, inspect the fuel pump and fuel filter.
  • Replace the fuel filter if clogged and ensure that the fuel pump is functioning correctly.
  • If injectors are clogged, use a fuel injector cleaner or replace them.

5. Inspect Engine Coolant Temperature Sensor

• Sub-steps:
  • Locate the coolant temperature sensor on the engine.
  • Disconnect the electrical connector and test the sensor with a multimeter.
  • Replace the sensor if the readings are outside of specifications.