how to fix P0171 code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, vacuum gauge, socket set, torque wrench, fuel pressure gauge, cleaning solution.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool before starting repairs.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Use a vacuum gauge to test the intake manifold for proper vacuum levels.
  3. Replace any damaged hoses or gaskets and reassemble.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor electrical connector.
  2. Remove the MAF sensor using the appropriate socket.
  3. Clean the MAF sensor with MAF cleaner or replace it if damaged.
  4. Reinstall the sensor and reconnect the electrical connector.

4. Test Fuel System

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail.
  2. Turn on the ignition without starting the engine and check the fuel pressure against specifications (usually around 30-40 psi).
  3. Replace the fuel filter if clogged, and if pressure is low, check the fuel pump and relay for faults.

5. Clean Throttle Body

• Sub-steps:
  1. Remove the air intake duct connected to the throttle body.
  2. Use throttle body cleaner and a soft cloth to clean the throttle body inside and out.
  3. Reinstall the duct and ensure all connections are secure.

6. Check Oxygen Sensors

• Sub-steps:
  1. Inspect the wiring and connectors of the upstream oxygen sensor for damage.
  2. Use a multimeter to test the sensor's voltage output while the engine is running.
  3. Replace the sensor if it is found to be faulty.