how to fix P0420 code on Honda Accord 10th Generation (2018-2022)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, infrared thermometer, socket set, jack and jack stands, safety glasses, gloves.
• Disconnect the negative terminal of the battery to prevent electrical shorts.
• Raise the vehicle using a jack and secure it on jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: Socket set, oxygen sensor socket.
  1. Locate the upstream (pre-catalytic) oxygen sensor and the downstream (post-catalytic) oxygen sensor.
  2. Disconnect the electrical connectors from both sensors.
  3. Use the oxygen sensor socket to remove the upstream sensor first, then the downstream sensor.
  4. Install the new oxygen sensors by threading them in by hand to avoid cross-threading, then tighten to manufacturer specifications (typically around 30-40 lb-ft).
  5. Reconnect the electrical connectors securely.

3. Check and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust pipe cutter or saw, new gaskets, torque wrench.
  1. Inspect the catalytic converter for signs of physical damage or blockage.
  2. If replacement is needed, disconnect the exhaust pipes from the catalytic converter using a socket set.
  3. Cut the exhaust pipe if necessary for removal (ensure to use a proper cutting tool).
  4. Install the new catalytic converter with new gaskets, ensuring all connections are tight and secure.
  5. Torque all bolts to manufacturer specifications.

4. Clear Codes and Reconnect Battery

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.