how to diagnose P0420 error code in Toyota Highlander XU70 (2020-Present)?

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the exhaust system to cool before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  • Use the O2 sensor socket to unscrew the sensor from the exhaust manifold.
  • Disconnect the electrical connector.
• Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the threads.
  • Hand-tighten the sensor and then use a torque wrench to tighten to manufacturer specifications (typically around 30 lb-ft).
• Repeat the process for the downstream (post-catalytic converter) oxygen sensor if necessary.

3. Inspect and Replace the Catalytic Converter

• Tools Required: Socket set, torque wrench, jack stands, exhaust pipe cutter (if needed).
• Inspect the catalytic converter for physical damage:
  • Check for dents, rust, or leaks.
• If replacement is needed:
  • Using the socket set, remove the bolts securing the catalytic converter to the exhaust system.
  • If applicable, cut the exhaust pipe using the exhaust pipe cutter.
  • Install the new catalytic converter, ensuring proper alignment.
  • Secure it with bolts and tighten to manufacturer specifications (usually around 40 lb-ft).

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Start the vehicle and allow it to idle for a few minutes.
• Use the OBD-II scanner to clear the P0420 code and any other related codes.