how to fix P0171 system too lean in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool down before starting the work.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines and intake components for cracks, breaks, or loose connections.
  2. Use a smoke machine or carburetor cleaner to detect leaks while the engine is running.
• Tools Required: Vacuum gauge, smoke machine, or carburetor cleaner.

3. Check and Clean the Mass Airflow Sensor

• Sub-steps:
  1. Remove the MAF sensor from the air intake duct.
  2. Clean the sensor using MAF cleaner spray; avoid touching the sensing elements.
  3. Reinstall the sensor and ensure all connections are secure.
• Tools Required: MAF cleaner spray, screwdriver set.

4. Test and Adjust Fuel Pressure

• Sub-steps:
  1. Connect the fuel pressure gauge to the fuel rail test port.
  2. Start the engine and observe the fuel pressure reading.
  3. If pressure is below specifications, check the fuel pump and filter; replace if necessary.
• Tools Required: Fuel pressure gauge.

5. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Remove the fuel injectors from the fuel rail.
  2. Use an injector cleaning kit to clean the injectors or replace them if clogged or damaged.
  3. Reinstall the injectors and ensure proper sealing.
• Tools Required: Injector cleaning kit, O-ring replacement kit.

6. Confirm Engine Coolant Temperature Sensor Function

• Sub-steps:
  1. Locate the coolant temperature sensor and disconnect the electrical connector.
  2. Use a multimeter to check resistance values at different temperatures against manufacturer specifications.
  3. Replace the sensor if it is out of specification.
• Tools Required: Multimeter.