how to troubleshoot P0171 code on Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool down before beginning work.

2. Inspect and Repair Air Intake System

• Sub-steps:
  1. Remove the engine cover, if applicable.
  2. Visually inspect the air intake duct and hoses for cracks or disconnections.
  3. Tighten any loose clamps or replace damaged components.
  4. Ensure the air filter is clean and replace if necessary.

3. Clean or Replace the MAF Sensor

• Sub-steps:
  1. Locate the MAF sensor in the air intake path.
  2. Disconnect the electrical connector and remove the sensor.
  3. Clean the MAF sensor with MAF cleaner spray; avoid touching the sensor element.
  4. Reinstall the cleaned or new MAF sensor and reconnect the electrical connector.

4. Check Fuel Pressure

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail's service port.
  2. Turn the ignition to the "ON" position (do not start) to check the fuel pressure.
  3. Compare the reading to the manufacturer's specification (usually around 40-50 psi).
  4. If pressure is low, check the fuel pump and filter for issues.

5. Inspect Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail assembly to access the injectors.
  2. Inspect each injector for clogs or leaks.
  3. Clean or replace any faulty injectors as necessary.
  4. Reassemble the fuel rail and reconnect the fuel lines.

6. Test Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) oxygen sensor.
  2. Use a multimeter to test sensor voltage output while the engine is running.
  3. If readings are outside of specifications, replace the oxygen sensor.

Tools Required:

• OBD-II scanner
• Multimeter
• Fuel pressure gauge
• MAF cleaner spray
• Socket set
• Screwdrivers

Parts Required:

• MAF sensor (if necessary)
• Fuel filter (if necessary)
• Fuel injectors (if necessary)
• Oxygen sensor (if necessary)

Estimated Repair Time: 2-4 hours

Safety Warnings:

• Disconnect the battery before working on electrical systems.
• Allow the engine to cool before opening any components.