how to fix P0171 code in Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Gather tools and parts needed for repairs.
• Disconnect the battery to prevent electrical shorts during the repair process.
• Tools Required: OBD-II scanner, vacuum gauge, fuel pressure gauge, MAF cleaner, socket set, multimeter.

2. Inspect and Repair Air Intake System

• Visually inspect all intake hoses and connections for cracks, tears, or loose fittings.
• Sub-steps:
  • Tighten any loose hose clamps.
  • Replace any damaged hoses or gaskets.
  • Conduct a smoke test if necessary to identify hidden vacuum leaks.

3. Fuel Pressure Check

• Connect the fuel pressure gauge to the fuel rail test port.
• Sub-steps:
  • Turn the ignition to the ON position without starting the engine and check the pressure reading against specifications (typically around 50-60 psi for most Toyota models).
  • If pressure is low, check the fuel pump and fuel filter for issues; replace if necessary.

4. MAF Sensor Cleaning/Replacement

• Locate the MAF sensor in the air intake duct.
• Sub-steps:
  • Disconnect the electrical connector from the MAF sensor.
  • Remove the MAF sensor using the appropriate socket.
  • Clean the sensor using MAF cleaner and let it dry, or replace it if damaged.

5. Fuel Injector Inspection

• Remove the injector connectors and test them using a multimeter for proper resistance.
• Sub-steps:
  • If injectors are found to be faulty, replace them with new units.
  • Ensure proper seating and sealing of the injectors during reinstallation.

6. Oxygen Sensor Check

• Inspect wiring and connectors of the upstream oxygen sensor for damage.
• Sub-steps:
  • Test the sensor using a multimeter to check for proper voltage output.
  • Replace the sensor if it is not functioning within the specified range.