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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, vacuum gauge, basic hand tools (sockets, wrenches), cleaning supplies (MAF cleaner).
• Disconnect the negative battery terminal to prevent electrical issues.

2. Inspect and Repair Intake Leaks

• Sub-steps:
  1. Visually inspect all intake hoses and the intake manifold for cracks or loose connections.
  2. Use a vacuum gauge to check for leaks in the vacuum lines.
  3. If any leaks are found, replace the affected hoses or gaskets.
  4. Reconnect all hoses securely.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor connector.
  2. Remove the MAF sensor from the intake duct.
  3. Clean the sensor using MAF cleaner. Avoid touching the sensor element.
  4. Allow the sensor to dry, then reinstall it. Ensure the connector is secure.

4. Check Fuel System

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail.
  2. Turn the ignition to the ON position (do not start) and check the fuel pressure against manufacturer specifications.
  3. If the pressure is low, check the fuel pump and filter. Replace if necessary.
  4. Reconnect the fuel pressure gauge after testing.

5. Test Oxygen Sensors

• Sub-steps:
  1. Use a multimeter to test the voltage output of the upstream oxygen sensor (should fluctuate between 0.1V and 0.9V).
  2. If the sensor is not functioning properly, replace it with an OEM equivalent.
  3. Clear the P0171 code using the OBD-II scanner after repairs.