how to fix P0171 code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts:
  • OBD-II scanner
  • Basic socket set
  • Screwdrivers
  • Multimeter
  • Cleaning supplies for MAF sensor (if applicable)
• Ensure the vehicle is parked on a level surface, and the engine is cool.

2. Inspect and Repair Air Intake System

• Step 1: Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
• Step 2: Use a smoke machine to test for vacuum leaks if visible inspection does not reveal any issues.
• Step 3: Replace any damaged hoses or components found during inspection.

3. Clean or Replace MAF Sensor

• Step 1: Locate the MAF sensor, typically found in the air intake duct between the air filter and throttle body.
• Step 2: Disconnect the electrical connector from the MAF sensor.
• Step 3: Remove the MAF sensor using the appropriate socket.
• Step 4: Clean the MAF sensor with MAF cleaner spray and allow it to dry. If damaged, replace it with a new sensor.
• Step 5: Reinstall the MAF sensor and reconnect the electrical connector.

4. Inspect Fuel System

• Step 1: Check the fuel filter for any signs of clogging; replace it if necessary.
• Step 2: Use a fuel pressure gauge to measure the fuel pressure at the rail. Compare it to the manufacturer's specifications.
• Step 3: If pressure is low, check the fuel pump for proper operation and replace it if faulty.

5. Test Fuel Injectors

• Step 1: Use a multimeter to check the resistance of each fuel injector according to specifications.
• Step 2: Inspect for any visible leaks around the fuel injectors.
• Step 3: Replace any faulty injectors as needed.

6. Verify Oxygen Sensor Function

• Step 1: Use a multimeter to check the voltage output of the upstream oxygen sensor while the engine is running.
• Step 2: If the sensor is not functioning within specified ranges, replace it.