how to fix P0171 lean condition on my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

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

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses and connections for cracks or disconnections.
  • Use a smoke machine or carburetor cleaner to identify leaks.
  • Replace any damaged hoses and re-tighten loose connections.

3. Clean or Replace the MAF Sensor

• Sub-steps:
  • Locate the MAF sensor in the air intake duct.
  • Disconnect the electrical connector and remove the sensor.
  • Clean the sensor with MAF cleaner and let it dry completely before reinstalling.
  • If damaged, replace the MAF sensor with a new unit.

4. Check and Replace Fuel Filter

• Sub-steps:
  • Locate the fuel filter and relieve fuel pressure by removing the fuel pump fuse and running the engine until it stalls.
  • Disconnect the fuel lines from the filter using a line wrench.
  • Replace the old filter with a new one, ensuring proper orientation.
  • Reconnect the fuel lines and reinstall the fuel pump fuse, then turn the ignition on to prime the system.

5. Test Fuel Pressure

• Sub-steps:
  • Connect a fuel pressure gauge to the fuel rail service port.
  • Turn the ignition to the ON position (do not start) and check the pressure reading against specifications (typically 50-60 psi for the Highlander).
  • If pressure is low, further investigate the fuel pump or regulator.

6. Reconnect Battery

• Reconnect the negative battery cable and ensure all connections are secure.