how to fix P0171 code in a Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Tools Required: OBD-II scanner, vacuum gauge, fuel pressure gauge, MAF cleaner, socket set, screwdriver set.
• Safety Warnings: Disconnect the battery before working on electrical systems and ensure the engine is cool before inspecting the intake.

2. Inspect for Vacuum Leaks

• Use a vacuum gauge to check for leaks in the intake manifold.
• Inspect vacuum hoses visually for cracks or disconnections.
• Apply carburetor cleaner around suspected areas and listen for changes in engine RPM.

3. Test Fuel Pressure

• Connect a fuel pressure gauge to the fuel rail service port.
• Turn the ignition to the "on" position without starting the engine and check the pressure reading; it should be within manufacturer specifications (typically 50-60 psi).
• If the pressure is low, inspect the fuel pump, filter, and relay.

4. Clean or Replace MAF Sensor

• Disconnect the MAF sensor electrical connector.
• Remove the MAF sensor from the intake duct.
• Use MAF sensor cleaner to clean the sensor elements, avoiding contact with other components.
• Reinstall the MAF sensor and reconnect the electrical connector.

5. Inspect Fuel Injectors

• Check for proper operation of the fuel injectors using a multimeter to test the resistance.
• If injectors are faulty, remove them and clean or replace them as necessary.
• Ensure that the fuel injector O-rings are not damaged during reinstallation.

6. Check Engine Coolant Temperature Sensor

• Locate the coolant temperature sensor and inspect the electrical connector for corrosion or damage.
• Test the sensor's resistance with a multimeter at various temperatures to ensure it is functioning correctly.
• Replace the sensor if out of specification.