how to fix the P0171 code on my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent any electrical shorts.
• Gather necessary tools and replacement parts.

2. Inspect and Repair Air Intake System

• Tools Required: Screwdriver set, torque wrench, vacuum gauge
• Inspect the air intake duct for cracks or loose connections. Replace any damaged components.
• Tighten or replace any loose clamps on the air intake hoses.
• Check the air filter and replace it if it's dirty.

3. Fuel Pressure Check

• Tools Required: Fuel pressure gauge
• Locate the fuel rail and connect the fuel pressure gauge to the service port.
• Turn the ignition on (without starting the engine) to prime the fuel pump.
• Check the fuel pressure reading against the manufacturer's specifications (typically between 40-50 psi). If low, replace the fuel pump or fuel filter as necessary.

4. Clean or Replace MAF Sensor

• Tools Required: MAF sensor cleaner or isopropyl alcohol
• Disconnect the MAF sensor wiring harness.
• Remove the MAF sensor from the air intake.
• Clean the sensor element using the MAF sensor cleaner. Allow it to dry completely before reinstalling.
• If cleaning does not resolve the issue, replace the MAF sensor.

5. Inspect Engine Coolant Temperature Sensor

• Tools Required: Multimeter
• Locate the engine coolant temperature sensor and disconnect the wiring harness.
• Use a multimeter to check the resistance of the sensor according to manufacturer specifications.
• Replace the sensor if it's out of specification.

6. Vacuum Leak Inspection

• Tools Required: Vacuum gauge, smoke machine (optional)
• Inspect all vacuum lines and intake manifold gaskets for leaks.
• Use a smoke machine to identify hard-to-find leaks if available.
• Replace any damaged hoses or gaskets.