how to diagnose P0420 code in my Toyota Highlander Fourth Generation (2020-present)?

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a level surface and engage the parking brake.
• Disconnect the negative battery terminal to ensure safety while working on electrical components.

2. Inspect Exhaust System

• Tools Required: Socket set, flashlight
• Remove any heat shields covering the catalytic converter and inspect for physical damage.
• Check for any exhaust leaks or holes in the pipes leading to and from the catalytic converter.

3. Test Oxygen Sensors

• Tools Required: Multimeter
• Reconnect the negative battery terminal.
• Locate the upstream and downstream oxygen sensors.
• Disconnect the sensors and measure the voltage output:
  • Upstream (Pre-Cat): Should fluctuate between 0.1V and 0.9V.
  • Downstream (Post-Cat): Should remain relatively steady around 0.5V to 0.7V.
• If the readings are outside these ranges, replace the faulty sensor.

4. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, wrench set, exhaust pipe cutter
• If the catalytic converter is found to be faulty:
  • Disconnect the exhaust pipes from the catalytic converter.
  • Remove the mounting bolts and brackets holding the catalytic converter.
  • Install the new catalytic converter, ensuring correct alignment.
  • Reattach the exhaust pipes and tighten all connections to the manufacturer's torque specifications.

5. Clear Codes and Test Drive

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Perform a test drive to verify if the check engine light returns.