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

Solution

1. Preparation

• Gather tools and parts:
  • OBD-II scanner
  • Fuel pressure gauge
  • MAF sensor cleaner
  • Basic hand tools (socket set, wrenches)
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Inspect Air Intake System

• Sub-steps:
  1. Visually inspect all vacuum hoses for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner around the intake manifold to locate any leaks.
  3. Tighten or replace any loose or damaged hoses.

3. Check Fuel Pressure

• Tools Required: Fuel pressure gauge
• Sub-steps:
  1. Connect the fuel pressure gauge to the fuel rail service port.
  2. Turn the ignition to the "ON" position (do not start) and check the pressure reading.
  3. Compare the reading against the manufacturer’s 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 MAF Sensor

• Tools Required: MAF sensor cleaner
• Sub-steps:
  1. Disconnect the electrical connector from the MAF sensor.
  2. Remove the MAF sensor from the intake duct.
  3. Spray the MAF sensor with MAF cleaner and allow it to dry completely.
  4. Reinstall the MAF sensor and reconnect the electrical connector.

5. Inspect Fuel Injectors

• Sub-steps:
  1. Check for fuel leaks around the injectors.
  2. Use an injector cleaner or perform an injector flow test to ensure they are functioning correctly.
  3. Replace any faulty injectors as necessary.

6. Check Engine Coolant Temperature Sensor

• Sub-steps:
  1. Locate the engine coolant temperature sensor (usually near the thermostat housing).
  2. Disconnect the connector and test the sensor's resistance using a multimeter.
  3. Compare the readings with the manufacturer's specifications. Replace if out of range.