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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, fuel pressure gauge, socket set, torque wrench, cleaning solvent, vacuum gauge.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool down before beginning repairs.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses and connections around the intake manifold and throttle body.
  2. Use a vacuum gauge to check for leaks; any readings significantly below the expected range indicate a leak.
  3. Replace any damaged or cracked hoses; ensure all connections are secure.

3. Clean MAF Sensor

• Sub-steps:
  1. Locate the MAF sensor (usually found between the air filter and the throttle body).
  2. Disconnect the electrical connector and remove the MAF sensor from the air intake duct.
  3. Spray MAF cleaner on the sensor elements; do not touch them with your fingers or any tools.
  4. Allow the sensor to dry completely before reinstallation.

4. Check and Adjust Fuel Pressure

• Sub-steps:
  1. Connect the fuel pressure gauge to the fuel rail Schrader valve.
  2. Turn the ignition key to the "ON" position (do not start the engine) and observe the fuel pressure reading.
  3. If the pressure is below the manufacturer's specification, inspect the fuel pump and fuel filter for faults.
  4. Replace the fuel filter if clogged and consider replacing the fuel pump if pressure is insufficient.

5. Inspect and Test Fuel Injectors

• Sub-steps:
  1. Use a multimeter to check the resistance of each fuel injector; compare readings to manufacturer specifications.
  2. If resistance is outside the specified range, replace the faulty injector.
  3. Clean any clogged injectors using an appropriate fuel injector cleaning solvent.