how to diagnose a P0420 code on my Toyota Highlander XU70 (2020-Present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, exhaust pressure gauge.
• Clear the error codes from the ECU after performing diagnostics to reset the check engine light.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Disconnect the negative battery terminal to prevent electrical shock.
  2. Locate the upstream and downstream oxygen sensors.
  3. Unplug the electrical connectors from both sensors.
  4. Use a socket wrench to remove the sensors from their locations.
  5. Install new oxygen sensors, applying anti-seize compound on the threads.
  6. Torque the sensors to the manufacturer's specification (usually around 30-40 lb-ft).
  7. Reconnect the electrical connectors and the negative battery terminal.

3. Inspect and Replace Catalytic Converter

• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Disconnect the exhaust pipes at the flanges before and after the catalytic converter.
  3. Remove mounting bolts using a socket set and detach the catalytic converter.
  4. Inspect the catalytic converter for signs of damage or blockages.
  5. Install the new catalytic converter, ensuring proper alignment with exhaust pipes.
  6. Torque the mounting bolts to manufacturer specifications (usually around 30-50 lb-ft).
  7. Reconnect exhaust pipes and ensure there are no leaks.

4. Clear Codes and Test

• Sub-steps:
  1. Use an OBD-II scanner to clear any active trouble codes.
  2. Start the engine and let it idle to check for any immediate issues.
  3. Take the vehicle for a test drive to ensure the check engine light does not reappear.