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

Solution

1. Preparation

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

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Use a smoke machine or propane torch (without igniting) to locate any vacuum leaks.
  3. Replace any damaged hoses or gaskets found during the inspection.

3. Clean or Replace MAF Sensor

• Sub-steps:
  1. Locate the MAF sensor on the air intake duct.
  2. Disconnect the electrical connector and remove the sensor from the duct.
  3. Clean the MAF sensor using MAF cleaner spray, following the manufacturer's instructions.
  4. If the sensor is damaged or heavily contaminated, replace it with a new one.

4. Check Fuel System

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail to measure fuel pressure.
  2. Compare the reading to the manufacturer's specifications; if low, check the fuel pump and filter.
  3. Replace the fuel filter if clogged and consider replacing the fuel pump if pressure is still inadequate.

5. Inspect Oxygen Sensors

• Sub-steps:
  1. Locate the upstream oxygen sensor (pre-catalytic converter).
  2. Remove the sensor using an oxygen sensor socket.
  3. Inspect the sensor for signs of contamination or damage; replace if necessary.
  4. Use a multimeter to test the sensor's response to changes in air-fuel mix.

6. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0171 code from the ECM.