what does it mean when my Toyota Highlander has a code P0171

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner to detect leaks while the engine is running.
  3. Replace any damaged hoses or gaskets found during inspection.

3. Clean or Replace Mass Air Flow Sensor

• Sub-steps:
  1. Locate the MAF sensor in the intake duct.
  2. Disconnect the electrical connector and remove the sensor.
  3. Clean the MAF sensor with MAF cleaner; do not touch the sensing element.
  4. If the sensor is defective, replace it with a new one.
  5. Reinstall the sensor and reconnect the electrical connector.

4. Inspect Fuel System

• Sub-steps:
  1. Check the fuel pressure with a fuel pressure gauge.
  2. Replace the fuel filter if it is clogged or has not been replaced as per maintenance schedule.
  3. Inspect fuel injectors for clogs or leaks; clean or replace as necessary.
  4. Listen for proper operation of the fuel pump while the ignition is in the "ON" position.

5. Test Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) oxygen sensor.
  2. Use a multimeter to check the voltage output; it should fluctuate between 0.1V to 0.9V.
  3. Replace the oxygen sensor if it shows a steady voltage or no output.