how to fix P0174 code in Toyota Corolla E170 (2013-2019)

Learn how to diagnose and fix P0174 lean air-fuel mixture issue in Toyota Corolla E170. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Repair Air Intake System

1. Visual Inspection
   • Check all vacuum hoses for cracks or disconnections.
   • Inspect the intake manifold gasket for any visible wear or leaks.
2. Testing for Vacuum Leaks
   • Use a smoke machine or carburetor cleaner to detect vacuum leaks while the engine is running.
3. Repair or Replace
   • Replace any damaged hoses or gaskets found during the inspection.

3. Test and Clean MAF Sensor

1. Remove MAF Sensor
   • Disconnect the wiring harness and unscrew the MAF sensor from the air intake duct.
2. Clean MAF Sensor
   • Use MAF sensor cleaner spray to clean the sensor element gently.
3. Reinstall MAF Sensor
   • Carefully reattach the MAF sensor and ensure all connections are secure.

4. Check and Adjust Fuel System

1. Fuel Pressure Test
   • Connect a fuel pressure gauge to the fuel rail and turn the ignition to the "ON" position to check the fuel pressure.
   • Compare the reading to the manufacturer’s specifications (typically around 40-50 psi).
2. Fuel Filter Replacement
   • If fuel pressure is low, replace the fuel filter and check fuel pump operation.

5. Oxygen Sensor Inspection

1. Visual Inspection
   • Check the wiring and connectors of the oxygen sensors for damage or corrosion.
2. Replace if Necessary
   • If the oxygen sensor appears faulty or is out of specifications, replace it.