how to fix P0420 code on my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool completely before beginning any work on the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet with extensions, torque wrench.
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Using the O2 sensor socket, carefully remove the upstream sensor.
  3. Install the new upstream oxygen sensor and torque it to the manufacturer's specifications (typically 30-35 ft-lbs).
  4. Repeat the process for the downstream oxygen sensor if it shows signs of failure.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust gasket (if needed).
• Sub-steps:
  1. Remove any heat shields or brackets securing the catalytic converter.
  2. Using a socket set, unfasten the bolts connecting the catalytic converter to the exhaust manifold and the exhaust pipe.
  3. Carefully lower the catalytic converter from the vehicle and inspect it for internal damage or blockage.
  4. Install the new catalytic converter, ensuring that any gaskets are properly aligned. Torque the bolts to the manufacturer's specifications (usually around 25-30 ft-lbs).
  5. Reattach any heat shields or brackets that were removed.

4. Reset the Engine Control Module (ECM)

• Tools Required: OBD-II scanner.
• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the ECM.
  3. Drive the vehicle for a few days to allow the ECM to recalibrate and monitor for recurring issues.