how to diagnose P0171 lean code in Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, vacuum gauge, socket set, torque wrench.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses and connections for cracks or disconnections.
  2. Use a vacuum gauge to test for leaks in the intake manifold.
  3. Replace any damaged hoses or gaskets identified during the inspection.

3. Check and Clean MAF Sensor

• Sub-steps:
  1. Locate the MAF sensor, typically found in the air intake duct.
  2. Disconnect the electrical connector and remove the MAF sensor from the duct.
  3. Clean the sensor element using MAF cleaner spray and a soft brush; allow it to dry completely.
  4. Reinstall the MAF sensor and reconnect the electrical connector.

4. Fuel System Inspection

• Sub-steps:
  1. Check the fuel pressure with a fuel pressure gauge; it should meet manufacturer specifications.
  2. If the pressure is low, inspect the fuel filter and fuel pump for clogs or failures; replace as necessary.
  3. Replace the fuel filter if it hasn't been changed recently (typically every 30,000 miles).

5. Oxygen Sensor Check

• Sub-steps:
  1. Inspect the wiring and connector of the upstream oxygen sensor for any damage or corrosion.
  2. Test the sensor with a multimeter to ensure it is functioning within specifications.
  3. Replace the oxygen sensor if it is not operating correctly.