how to diagnose P0420 catalyst efficiency issue on Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, smoke machine (if available).
• Disconnect the battery to ensure safety.

2. Oxygen Sensor Replacement (if faulty)

• Remove the negative battery terminal.
• Locate the upstream and downstream oxygen sensors.
• Using the appropriate socket, unscrew the faulty oxygen sensor(s).
• Apply anti-seize compound to the threads of the new sensor.
• Install the new sensor and torque to manufacturer specifications (usually around 30 ft-lbs).
• Reconnect the battery and clear codes using the OBD-II scanner.

3. Catalytic Converter Replacement (if necessary)

• Safely elevate the vehicle and secure it with jack stands.
• Remove heat shields if present to access the catalytic converter.
• Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe using a socket wrench.
• Inspect and clean the mating surfaces of the exhaust system.
• Install the new catalytic converter, ensuring proper alignment and sealing.
• Torque the bolts to manufacturer specifications (check service manual for specific values).
• Reinstall any heat shields that were removed.

4. Final Checks

• Reconnect the battery terminal.
• Start the engine and allow it to reach operating temperature.
• Use the OBD-II scanner to confirm that the P0420 code has been cleared and that no new codes appear.