how to fix P0420 code on my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

1. Locate the oxygen sensors: Identify the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Remove the upstream oxygen sensor:
   • Use an oxygen sensor socket to unscrew and remove the upstream sensor.
   • Inspect the sensor for carbon buildup or damage.
3. Replace if necessary: If the sensor is faulty, install a new one, ensuring it is properly threaded and tightened to the manufacturer's torque specifications (typically around 30 lb-ft).
4. Remove the downstream oxygen sensor: Repeat the process for the downstream sensor, checking for similar issues.

3. Inspect the Catalytic Converter

1. Visual Inspection: Check for dents, cracks, or rust on the catalytic converter.
2. Performance Test: If the converter appears intact, perform a back pressure test using a pressure gauge to ensure it's within acceptable limits (typically less than 2.0 psi at 2,500 RPM).
3. Replace if necessary: If back pressure is high or the converter is damaged, remove the old converter by unbolting it from the exhaust pipe and installing a new one. Torque bolts to specifications (generally around 40 lb-ft).

4. Clear Codes and Test Drive

1. Reconnect the battery: Once repairs are completed, reconnect the negative battery terminal.
2. Clear the error codes: Use the OBD-II scanner to erase the P0420 code.
3. Test drive: Take the vehicle for a test drive to ensure the check engine light does not reappear and monitor performance.