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

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Raise and support the vehicle using jack stands if necessary.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Sub-steps:
  1. Locate the upstream (pre-cat) and downstream (post-cat) oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Using an oxygen sensor socket, carefully remove the sensors from the exhaust manifold and catalytic converter.
  4. Install new oxygen sensors by threading them into their respective locations and tightening to manufacturer specifications (generally around 30 ft-lbs).
  5. Reconnect the electrical connectors to the oxygen sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. Locate the catalytic converter in the exhaust system.
  2. Disconnect the exhaust pipes before and after the catalytic converter using a socket set.
  3. Remove any heat shields or brackets holding the catalytic converter in place.
  4. Install the new catalytic converter, making sure to align it properly with the exhaust pipes.
  5. Tighten all connections to the manufacturer’s torque specifications.
  6. Reinstall any heat shields or brackets that were removed.

4. Reset the Engine Control Module (ECM)

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use an OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and allow it to idle for several minutes to ensure the system is functioning correctly.