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

Solution

1. Preparation

• Tools Required: OBD-II scanner, vacuum gauge, multimeter, fuel pressure gauge, basic hand tools.
• Safety Warnings: Disconnect the battery before working on electrical systems. Allow the engine to cool before performing any inspections.

2. Inspect and Clean MAF Sensor

• Remove the MAF sensor from the intake tube.
• Use MAF cleaner spray to clean the sensor elements.
• Allow to dry completely before reinstalling.
• Reconnect the MAF sensor.

3. Repair or Replace Vacuum Hoses

• Identify any damaged or cracked vacuum hoses during inspection.
• Replace any faulty hoses with OEM parts to ensure proper fit and function.
• Ensure all hoses are securely connected.

4. Test and Repair Fuel System

• Fuel Pressure: Connect the fuel pressure gauge to the fuel rail and turn the ignition to the "on" position without starting the engine. Compare the reading to manufacturer specifications.
  • If the pressure is low, check the fuel pump and fuel filter and replace as necessary.
• Fuel Injectors: If injectors are leaking or not operating, remove and clean or replace them as needed.

5. Inspect Intake Manifold Gasket

• Remove the intake manifold if leaks are suspected.
• Replace any damaged gaskets with new OEM gaskets.
• Reinstall the intake manifold, ensuring proper torque specifications are followed.

6. Check ECT Sensor

• Disconnect the ECT sensor and check resistance with a multimeter according to temperature specifications.
• Replace the sensor if readings are outside the acceptable range.