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

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool down completely before proceeding.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses and connections for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner while the engine is running to identify leaks.
  3. Replace any damaged hoses or gaskets found during inspection.

3. Check and Replace the MAF Sensor (if necessary)

• Sub-steps:
  1. Disconnect the MAF sensor connector.
  2. Remove the MAF sensor using a Torx driver or socket set.
  3. Clean the MAF sensor using MAF sensor cleaner or isopropyl alcohol; avoid touching the sensor element.
  4. If cleaning does not resolve the issue, replace the MAF sensor with a new one.

4. Fuel System Inspection

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail service port.
  2. Turn the ignition key to the "ON" position to prime the fuel system and check the pressure reading.
  3. If pressure is below specification (generally around 35-50 psi), inspect the fuel pump, filter, and lines for issues; replace components as necessary.

5. Inspect Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail assembly to access the injectors (ensure fuel pressure is relieved first).
  2. Inspect injectors for clogs or leaks; clean or replace as needed.
  3. Reinstall the fuel rail and ensure all connections are secure.

6. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0171 code.
• Start the engine and allow it to idle to check for proper operation.