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

Solution

1. Preparation

• Gather tools and parts.
• Ensure the vehicle is parked on a level surface with the engine off.
• Disconnect the negative battery terminal.

2. Inspect and Repair Vacuum Leaks

• Tools Required: Visual inspection tools, vacuum gauge
  1. Visually inspect all vacuum hoses for cracks or disconnections.
  2. Use a vacuum gauge to check for any leaks; if leaks are found, replace the faulty hoses or gaskets.

3. Check Fuel Pressure

• Tools Required: Fuel pressure gauge
  1. Connect the fuel pressure gauge to the fuel rail test port.
  2. Turn the ignition to the "ON" position without starting the engine and observe the pressure reading.
  3. Compare the reading to manufacturer specifications (typically around 50-60 psi for most Toyota engines).
  4. If the pressure is low, inspect the fuel pump and filter for issues.

4. Clean or Replace the MAF Sensor

• Tools Required: MAF cleaner, Torx screwdriver
  1. Locate the MAF sensor in the intake duct.
  2. Disconnect the electrical connector.
  3. Remove the sensor using the Torx screwdriver.
  4. Clean the sensor with MAF cleaner and let it dry.
  5. Reinstall the sensor and reconnect the electrical connector.

5. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
  1. Use the OBD-II scanner to monitor live data for the oxygen sensors.
  2. If the readings are sluggish or not switching between rich and lean, consider replacing the affected sensor(s).

6. Reassemble and Check

• Reconnect the negative battery terminal.
• Start the engine and check for any exhaust leaks and ensure all components are secure.