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

Solution

1. Preparation

• Gather necessary tools and safety equipment.
• Disconnect the battery to prevent electrical shorts during the repair.
• Ensure the engine is cool before beginning work.

2. Inspect and Repair Air Intake System

1. Remove the engine cover (if applicable) using a socket set.
2. Check all intake hoses for cracks or loose connections; replace any damaged hoses.
3. Inspect the intake manifold gasket for leaks; replace if worn.

3. Fuel System Inspection

1. Connect a fuel pressure gauge to the Schrader valve on the fuel rail.
2. Turn the ignition to the "ON" position (do not start) and check the fuel pressure reading.
   • If the pressure is below specifications (generally around 50-60 psi for most Toyota engines), inspect the fuel pump and filter.
3. If necessary, replace the fuel pump or fuel filter as per manufacturer specifications.

4. MAF Sensor Cleaning/Replacement

1. Locate the MAF sensor in the air intake duct.
2. Carefully disconnect the electrical connector from the MAF sensor.
3. Remove the sensor using a Torx screwdriver.
4. Clean the MAF sensor with MAF cleaner spray; allow it to dry completely.
5. If damaged, replace with a new MAF sensor.

5. Check and Replace Vacuum Lines

1. Inspect all vacuum lines connected to the intake manifold and other components.
2. Replace any cracked or damaged vacuum hoses.
3. Reconnect all lines securely.

6. Reassemble and Clear Codes

1. Reinstall any components removed during the inspection.
2. Reconnect the battery.
3. Use the OBD-II scanner to clear the P0171 code from the ECM.