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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Vacuum gauge, hose clamps, RTV silicone sealant
  • Visually inspect all vacuum hoses, intake manifold gaskets, and throttle body gaskets for cracks or wear.
  • Use a vacuum gauge to check for leaks; perform a smoke test if necessary.
  • Replace any damaged hoses or gaskets, and use RTV silicone sealant if applicable to ensure a proper seal.

3. Clean or Replace Mass Air Flow Sensor

• Tools Required: MAF cleaner, screwdriver set
  • Locate the MAF sensor in the intake duct.
  • Disconnect the electrical connector and remove the sensor using the appropriate screwdriver.
  • Clean the sensor with MAF cleaner, ensuring not to touch the sensing element.
  • If the sensor is damaged, replace it with a new one.

4. Check Fuel Pressure

• Tools Required: Fuel pressure gauge
  • Locate the fuel pressure test port on the fuel rail.
  • Connect the fuel pressure gauge and turn the ignition to the "ON" position (do not start the engine) to check the fuel pressure.
  • Compare the reading with the manufacturer’s specifications; if low, inspect the fuel pump and filter for issues.

5. Inspect Oxygen Sensors

• Tools Required: Multimeter or OBD-II scanner
  • Locate the upstream oxygen sensor (bank 1).
  • Use a multimeter to check voltage output (should oscillate between 0.1V and 0.9V).
  • If the sensor is malfunctioning, replace it with a new unit.

6. Clear Codes and Test Drive

• Reconnect the battery and use the OBD-II scanner to clear the P0171 code.
• Perform a test drive to ensure the code does not reappear and monitor engine performance.