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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the vehicle's battery to ensure safety during electrical work.
• Allow the engine to cool completely before starting any work.

2. Inspect and Repair Air Intake System

• Tools Required: Socket set, screwdriver set
• Instructions:
  1. Remove the engine cover if applicable.
  2. Inspect the air intake hoses for cracks or loose connections; replace any damaged hoses.
  3. Check the throttle body for carbon buildup; clean it using throttle body cleaner if necessary.

3. Clean or Replace MAF Sensor

• Tools Required: MAF sensor cleaner, screwdriver set
• Instructions:
  1. Locate the MAF sensor on the air intake duct.
  2. Disconnect the electrical connector and remove the sensor.
  3. Clean the sensor using MAF sensor cleaner; allow it to dry completely.
  4. Reinstall the MAF sensor and reconnect the electrical connector.

4. Test Fuel Pressure

• Tools Required: Fuel pressure gauge
• Instructions:
  1. Locate the fuel rail and connect the fuel pressure gauge to the test port.
  2. Turn the ignition to the "ON" position (do not start the engine) and check the pressure reading.
  3. Compare the reading with manufacturer specifications; if it's low, check the fuel pump and filter for issues.

5. Inspect Fuel Injectors

• Tools Required: Noid light, multimeter
• Instructions:
  1. Connect a noid light to the injector harness to check for proper signal.
  2. If there's no signal, check the wiring and connectors for damage.
  3. If the signal is present, remove the injectors and inspect them for clogs; clean or replace as needed.

6. Check Engine Coolant Temperature Sensor

• Tools Required: Multimeter, socket set
• Instructions:
  1. Locate the engine coolant temperature sensor and disconnect the electrical connector.
  2. Use a multimeter to test the resistance of the sensor; compare with manufacturer specifications.
  3. Replace the sensor if it is outside the specified range.