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

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, thermocouple, socket set, and safety glasses.
• Ensure the vehicle is parked on a level surface and the engine is turned off.

2. Inspect and Replace Oxygen Sensors

• Remove the upstream oxygen sensor (pre-catalytic converter):

  • Disconnect the electrical connector.
  • Use a socket wrench to unscrew the sensor.
  • Install the new sensor and reconnect the electrical connector.

• Remove the downstream oxygen sensor (post-catalytic converter):

  • Repeat the process as with the upstream sensor.
  • Ensure it is properly seated and connected.

3. Replace Catalytic Converter (if necessary)

• Remove the exhaust components:

  • Disconnect the exhaust pipe from the catalytic converter using a socket set.
  • Remove any brackets or hangers holding the catalytic converter in place.

• Install the new catalytic converter:

  • Position the new converter, ensuring proper alignment with the exhaust system.
  • Reattach all brackets and hangers, and reconnect the exhaust pipe.
  • Torque all bolts to manufacturer specifications (typically around 30-35 lb-ft but check specific values).

4. Clear Codes and Test

• Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
• Test drive the vehicle to ensure the check engine light does not reappear and monitor performance.