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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, jack and jack stands.

2. Inspect and Replace Oxygen Sensors (if needed)

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors on the exhaust system.
  2. Use a socket wrench to unbolt the oxygen sensors from their mounting points.
  3. Disconnect the wiring harness from each oxygen sensor.
  4. Install the new oxygen sensors by reversing the removal steps. Ensure they are torqued to the manufacturer’s specifications (typically around 30-35 ft-lbs).
  5. Reconnect the wiring harness to the new sensors.

3. Inspect and Replace the Catalytic Converter (if necessary)

• Sub-steps:
  1. If the catalytic converter is damaged or clogged, remove the exhaust pipe(s) leading to it.
  2. Unbolt the catalytic converter from the exhaust manifold and from the downstream exhaust pipe using a socket set.
  3. Install the new catalytic converter, ensuring all gaskets are replaced and that it is properly aligned with the exhaust system.
  4. Torque all bolts according to the manufacturer's specifications.
  5. Reattach the exhaust pipe(s) and check for proper alignment and fit.

4. Reset the Engine Control Module (ECM)

• Sub-steps:
  1. Reconnect the battery terminals.
  2. Use an OBD-II scanner to erase the trouble codes stored in the ECM.
  3. Start the engine and allow it to reach operating temperature.