how to fix P0171 code in Toyota Highlander Third Generation (2014-2019)?

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative terminal of the battery.
• Ensure the engine is cool before beginning work.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect vacuum hoses for cracks or disconnections.
  2. Use a smoke machine to identify any hidden leaks if necessary.
  3. Replace any damaged hoses or gaskets.
• Tools Required: Smoke machine, basic hand tools.

3. Clean or Replace Mass Airflow Sensor (MAF)

• Sub-steps:
  1. Locate the MAF sensor in the air intake duct.
  2. Disconnect the electrical connector and remove the sensor.
  3. Clean the MAF sensor with MAF cleaner or replace it if damaged.
  4. Reinstall the sensor and reconnect the electrical connector.
• Tools Required: Torx or socket set, MAF cleaner.

4. Check and Repair Fuel System

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail.
  2. Turn the ignition to the "ON" position (not starting the engine) to check the pressure.
  3. If pressure is low, check the fuel pump operation and replace if necessary.
  4. Inspect fuel filters for clogs and replace if needed.
• Tools Required: Fuel pressure gauge, basic hand tools.

5. Inspect Fuel Injectors

• Sub-steps:
  1. Remove the fuel injectors from the fuel rail.
  2. Clean the injectors using an ultrasonic cleaner or replace them if they show signs of failure.
  3. Reinstall the cleaned or new injectors and ensure proper sealing.
• Tools Required: Ultrasonic cleaner, basic hand tools.

6. Verify Engine Coolant Temperature Sensor

• Sub-steps:
  1. Locate the engine coolant temperature sensor.
  2. Use a multimeter to check the resistance and compare it to specifications.
  3. Replace the sensor if readings are out of range.
• Tools Required: Multimeter, basic hand tools.