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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum lines for cracks or disconnections.
  • Use a smoke machine or carburetor cleaner to check for leaks at the intake manifold and around the throttle body.
  • Replace any damaged vacuum lines or gaskets.

3. Clean or Replace MAF Sensor

• Sub-steps:
  • Locate the MAF sensor in the air intake duct.
  • Disconnect the electrical connector and remove the sensor.
  • Clean the MAF sensor with MAF cleaner, ensuring not to touch the sensor element.
  • If the sensor is damaged, replace it with a new one and reconnect.

4. Check Fuel System

• Sub-steps:
  • Connect a fuel pressure gauge to the fuel rail.
  • Turn the ignition to the "ON" position (do not start) and check the pressure reading.
  • If pressure is below specifications (usually around 50-60 psi), inspect the fuel pump, fuel filter, and fuel lines for issues.
  • Replace any faulty components as necessary.

5. Inspect Oxygen Sensors

• Sub-steps:
  • Check the wiring and connectors of the upstream oxygen sensor for damage.
  • Use a multimeter to test the sensor’s voltage and response time (this may require a specialized procedure based on the sensor type).
  • Replace the sensor if it fails the tests.