how to fix P0171 lean code in Toyota Corolla E170 (2013-2019)

Solution

1. Preparation

• Gather tools and parts required.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Ensure the engine is cool before beginning work.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  • Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  • Use a smoke machine or carburetor cleaner to check for leaks. If the idle changes, a leak is present.
  • Replace any damaged hoses with OEM parts.

3. Fuel System Inspection

• Sub-steps:
  • Connect a fuel pressure gauge to the fuel rail.
  • Turn the ignition to the ON position (do not start) and observe the pressure reading. It should be within the manufacturer's specification (usually 30-40 psi).
  • If pressure is low, check the fuel pump, fuel filter, and fuel lines for blockages or failures. Replace as needed.

4. Clean or Replace MAF Sensor

• Sub-steps:
  • Locate the MAF sensor in the air intake duct.
  • Remove the electrical connector and unscrew the sensor.
  • Use MAF cleaner to carefully clean the sensor element. Do not touch the sensor with fingers.
  • If cleaning does not resolve the issue, replace the MAF sensor with a new one.

5. Inspect Fuel Injectors

• Sub-steps:
  • Remove the fuel rail and inspect injectors for clogs.
  • Clean injectors using a specialized injector cleaning kit or replace them if they are faulty.
  • Reinstall the fuel rail and ensure proper seating of injectors.

6. Check Oxygen Sensors

• Sub-steps:
  • Locate the upstream oxygen sensor (pre-catalytic converter).
  • Use a multimeter to test the sensor's voltage output while the engine is running; it should fluctuate between 0.1V to 0.9V.
  • Replace the sensor if it is not functioning properly.