how to fix the P0171 code in my Toyota Highlander Third Generation (2014-2019)?

Solution

1. Preparation

• Tools Required: OBD-II scanner, vacuum gauge, fuel pressure gauge, basic socket set, MAF cleaner, safety glasses, gloves
• Disconnect the negative battery cable to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Visually check all vacuum hoses and the intake manifold for cracks or loose connections.
• Use a vacuum gauge to test for leaks; a steady reading indicates no leaks.
• If leaks are found, replace damaged hoses or reseal connections.

3. Clean or Replace the MAF Sensor

• Remove the MAF sensor from the air intake duct.
• Use MAF cleaner to spray the sensor carefully; avoid touching the sensor element.
• Allow it to dry completely before reinstalling.
• If cleaning does not resolve the issue, consider replacing the MAF sensor.

4. Check Fuel Pressure

• Connect the fuel pressure gauge to the fuel rail test port.
• Turn the ignition to the "ON" position without starting the engine and observe the pressure reading.
• Compare the reading with the manufacturer’s specifications; if it's low, inspect the fuel pump and fuel filter for faults.

5. Inspect and Clean Fuel Injectors

• If fuel pressure is correct, remove the fuel injectors for inspection.
• Check for clogs or dirt; use a fuel injector cleaning kit if necessary.
• Reinstall or replace any faulty injectors.

6. Test Engine Coolant Temperature Sensor

• Locate and disconnect the engine coolant temperature sensor.
• Use a multimeter to check the sensor's resistance; compare it with manufacturer specifications.
• Replace the sensor if it is out of range or faulty.