how to diagnose P0171 code on Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery before starting any repairs.
• Allow the engine to cool down if it has been running.

2. Inspect and Repair Vacuum Leaks

• Visually inspect all vacuum hoses and connections for cracks or disconnections.
• Use smoke testing if necessary to identify hard-to-find leaks.
• Replace any damaged hoses or re-secure loose connections as needed.

3. Clean or Replace MAF Sensor

• Disconnect the electrical connector from the MAF sensor.
• Remove the MAF sensor from the air intake duct using the appropriate socket size.
• Clean the MAF sensor using MAF sensor cleaner. Avoid touching the sensor elements.
• If the sensor is faulty, install a new MAF sensor following manufacturer specifications.

4. Verify Fuel Pressure

• Connect a fuel pressure gauge to the fuel rail test port.
• Turn the ignition key to the "ON" position without starting the engine and check the pressure reading.
• Compare the reading to the manufacturer's specified fuel pressure. If it is low, check the fuel pump and fuel filter.

5. Inspect Fuel Injectors

• Check the fuel injectors for any signs of leaks or clogs.
• Use a multimeter to test the resistance of the injectors; replace any that are out of specification.
• If injectors are clogged, use a fuel injector cleaner or replace them if necessary.

6. Test and Replace Coolant Temperature Sensor (if needed)

• Locate the engine coolant temperature sensor and disconnect its electrical connector.
• Use a multimeter to measure the resistance of the sensor at various temperatures.
• If readings are outside of specification, replace the sensor with a new one.