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

Solution

1. Preparation

• Gather tools and parts needed for repair.
• Disconnect the negative battery terminal to prevent electrical shock.
• Ensure the vehicle is on a level surface and properly secured.

2. Inspect and Repair Air Intake System

• Sub-steps:
  1. Visually inspect all hoses and connections in the air intake system for cracks or disconnections.
  2. Replace any damaged hoses or gaskets identified during inspection.
  3. Tighten any loose clamps and fittings.

3. Test Fuel Pressure

• Sub-steps:
  1. Connect a fuel pressure gauge to the fuel rail service port.
  2. Turn the ignition on (do not start the engine) and check the fuel pressure reading; it should match the specifications (typically 43-50 psi for most models).
  3. If pressure is low, check the fuel pump, filter, and relay for issues; replace any faulty components.

4. Clean or Replace MAF Sensor

• Sub-steps:
  1. Disconnect the MAF sensor connector and remove the sensor from the intake tube.
  2. Clean the sensor with MAF sensor cleaner; do not touch the sensor elements.
  3. If cleaning does not resolve the issue, replace the MAF sensor with an OEM equivalent.

5. Inspect Oxygen Sensors

• Sub-steps:
  1. Locate the upstream oxygen sensor and inspect its wiring and connector for damage.
  2. Use a multimeter to check the sensor’s voltage output while the engine is running; it should fluctuate between 0.1 to 0.9 volts.
  3. Replace the sensor if it exhibits faulty readings or physical damage.

6. Check Engine Coolant Temperature Sensor

• Sub-steps:
  1. Disconnect the connector from the coolant temperature sensor.
  2. Use a multimeter to measure resistance; compare the readings with manufacturer specifications at various temperatures.
  3. Replace the sensor if readings are out of range.