how to fix P0174 code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, vacuum gauge, fuel pressure gauge, MAF sensor cleaner, socket set, torque wrench.
• Disconnect the negative battery cable to prevent electrical shorts.

2. Inspect and Repair Vacuum Leaks

• Sub-steps:
  1. Use a vacuum gauge to check for leaks in the intake system.
  2. Inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
  3. Replace any damaged hoses and reattach any loose connections.
  4. Reconnect the negative battery cable.

3. Fuel System Inspection

• Sub-steps:
  1. Attach the fuel pressure gauge to the fuel rail.
  2. Turn the ignition key to the ON position (do not start) to check fuel pressure; it should meet manufacturer specifications (typically 40-50 psi).
  3. If pressure is low, check the fuel pump, filter, and relay for issues; replace as necessary.

4. MAF Sensor Cleaning or Replacement

• Sub-steps:
  1. Locate the MAF sensor, which is usually found between the air filter and throttle body.
  2. Carefully disconnect the electrical connector and remove the MAF sensor from its housing.
  3. Spray MAF sensor cleaner onto the sensing elements while avoiding contact with other components.
  4. Allow it to dry completely, then reinstall the sensor and reconnect the electrical connector.

5. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Disconnect the fuel injector connectors and remove the fuel rail with injectors attached.
  2. Inspect the injectors for clogs or signs of wear. Clean them using a professional injector cleaning kit or replace them if damaged.
  3. Reinstall the fuel rail with injectors and reconnect connectors.

6. Oxygen Sensor Check

• Sub-steps:
  1. Use the OBD-II scanner to monitor the oxygen sensor readings while the engine is running.
  2. If readings are erratic or outside of the normal range, replace the oxygen sensor.
  3. Reconnect the battery and clear the codes from the ECM.