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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative terminal of the battery to prevent electrical shorts.
• Allow the engine to cool down if it has been running.

2. Inspect and Clean MAF Sensor

• Tools Required: Torx screwdriver, MAF cleaner
• Remove the MAF sensor from the air intake duct using the Torx screwdriver.
• Spray the MAF cleaner on the sensor elements without touching them.
• Allow the sensor to dry completely before reinstalling.
• Reinstall the MAF sensor securely.

3. Check for Vacuum Leaks

• Tools Required: Smoke machine or propane torch (without igniting), vacuum gauge
• Use a smoke machine to introduce smoke into the intake system and observe for any leaks.
• Alternatively, use a propane torch (unlit) around vacuum hoses and intake manifold while monitoring engine RPM changes.
• Tighten loose connections and replace any damaged hoses.

4. Test Fuel Pressure

• Tools Required: Fuel pressure gauge
• Locate the fuel pressure test port on the fuel rail.
• Connect the fuel pressure gauge and turn the ignition to the "ON" position without starting the engine to check pressure readings.
• Compare the readings to manufacturer specifications (typically 40-50 psi for most systems).
• If pressure is low, inspect the fuel pump and filter for issues.

5. Inspect and Repair Air Intake System

• Visually inspect the air intake duct for any cracks or damage.
• Ensure all clamps and connections are tight.
• Replace any damaged components as necessary.

6. Clear Codes and Test Drive

• Use the OBD-II scanner to clear the P0171 code.
• Test drive the vehicle to monitor if the check engine light returns and to evaluate performance.