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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses and connections for cracks or disconnections.
  • Use a smoke machine or carburetor cleaner to identify leaks by spraying around the intake manifold and vacuum hoses.
  • Replace any damaged hoses or seals.

3. Clean or Replace the Mass Airflow Sensor

• Tools Required: MAF cleaner, screwdriver
• Sub-steps:
  • Disconnect the MAF sensor electrical connector.
  • Remove the MAF sensor from the air intake duct using a screwdriver.
  • Clean the sensor with MAF cleaner and allow it to dry completely.
  • Reinstall the MAF sensor and reconnect the electrical connector.

4. Check Fuel Pressure

• Tools Required: Fuel pressure gauge, wrenches
• Sub-steps:
  • Locate the fuel pressure test port on the fuel rail.
  • Connect the fuel pressure gauge to the test port.
  • Turn the ignition switch to the "ON" position (do not start the engine) and check the pressure reading.
  • If pressure is below specifications (typically around 40-50 psi), check the fuel pump and filter for issues.

5. Inspect Fuel Injectors

• Tools Required: Multimeter, fuel injector cleaner (if needed)
• Sub-steps:
  • Disconnect the fuel injector electrical connectors.
  • Use a multimeter to check the resistance of each injector (should typically be around 12-16 ohms).
  • If any injectors are out of specification, replace them.
  • Clean the fuel injectors using a fuel injector cleaner if they are clogged.

6. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0171 code and any other stored codes.