how to diagnose P0420 code on Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

1. Inspect Wiring and Connectors:

   • Check for frayed wires or loose connections at the upstream and downstream oxygen sensors.
   • Repair or replace any damaged wiring.

2. Remove Oxygen Sensors:

   • Use an oxygen sensor socket to unscrew the upstream and downstream sensors.
   • Take care not to damage the threads in the exhaust manifold or catalytic converter.

3. Install New Oxygen Sensors:

   • Apply anti-seize compound to the threads of the new sensors (if required).
   • Torque the sensors to manufacturer's specifications (typically around 30 lb-ft).
   • Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Visual Inspection:

   • Check for physical signs of damage or blockage in the catalytic converter.

2. Remove Old Catalytic Converter:

   • Loosen and remove the bolts or clamps securing the catalytic converter to the exhaust system.
   • Carefully lower and remove the catalytic converter.

3. Install New Catalytic Converter:

   • Position the new catalytic converter in place, ensuring proper alignment with exhaust pipes.
   • Secure with bolts or clamps, torquing to manufacturer specifications.

4. Reset the Engine Control Module (ECM)

• Reconnect the battery.
• Use the OBD-II scanner to clear the P0420 code and reset the ECM.

5. Test Drive Vehicle

• Drive the vehicle under various conditions to ensure the check engine light does not return.