how to fix the P0420 code on my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Sub-steps:
  1. Identify the upstream and downstream oxygen sensors.
  2. Disconnect the wiring harness from the sensors.
  3. Use the O2 sensor socket to remove the sensors from the exhaust manifold and catalytic converter.
  4. Install the new oxygen sensors by screwing them in by hand and then torqueing to the manufacturer’s specifications (usually around 30 ft-lbs).
  5. Reconnect the wiring harness.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if needed)
• Sub-steps:
  1. Remove any heat shields if present, using the socket set.
  2. Disconnect the exhaust pipes from the catalytic converter using the socket set (may require cutting if rusted).
  3. Remove the catalytic converter from its mounting brackets.
  4. Install the new catalytic converter, ensuring it is properly aligned.
  5. Reconnect the exhaust pipes and torque to manufacturer's specifications.
  6. Reinstall any heat shields removed earlier.

4. Reset the Engine Control Module (ECM)

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and let it idle for a few minutes.