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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors

1. Locate the Oxygen Sensors
   • Identify the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Remove the Oxygen Sensors
   • Use an oxygen sensor socket to carefully unscrew the sensors.
   • Disconnect the electrical connectors from each sensor.
3. Install New Oxygen Sensors
   • Apply anti-seize compound to the threads of the new sensors (if needed).
   • Screw in the new sensors and reconnect the electrical connectors.
   • Torque the sensors to the manufacturer's specifications (usually around 30-40 Nm).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove the Exhaust Components
   • Unscrew the bolts securing the catalytic converter to the exhaust manifold and the exhaust pipe.
   • Carefully lower the catalytic converter from the vehicle.
2. Install New Catalytic Converter
   • Position the new catalytic converter in place and secure it with bolts.
   • Torque the bolts to the manufacturer's specifications (usually around 40-50 Nm).
3. Reinstall Any Removed Components
   • Reattach any heat shields or exhaust hangers that were removed during the process.

4. Finalize the Repair

1. Reconnect the Battery
   • Reconnect the negative battery terminal.
2. Clear Error Codes
   • Use the OBD-II scanner to clear the P0420 code.
3. Test Drive the Vehicle
   • Drive the vehicle for a short distance (at least 10-15 miles) to monitor for any reoccurrence of the code.