how to fix P0420 code on Honda Accord Eleventh Generation (2023-present)

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the negative battery terminal to ensure safety.
• Allow the engine to cool completely before starting work.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream (pre-catalytic) oxygen sensor:
  1. Locate the sensor on the exhaust manifold.
  2. Use the O2 sensor socket to unscrew the sensor.
  3. Install the new sensor and torque to the manufacturer’s specification (usually around 30 lb-ft).
• Repeat for the downstream (post-catalytic) oxygen sensor, if required.

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

• Tools Required: Socket set, torque wrench, exhaust pipe cutter
• If the catalytic converter is damaged:
  1. Remove the exhaust pipes connected to the catalytic converter using a socket set.
  2. Cut the exhaust pipe if necessary to remove the old catalytic converter.
  3. Install the new catalytic converter, ensuring proper alignment.
  4. Reattach the exhaust pipes and torque to manufacturer specifications.

4. Inspect Exhaust System for Leaks

• Tools Required: Exhaust leak detector, visual inspection tools
• Perform a smoke test or use a visual inspection to find leaks:
  1. Inspect all joints and welds in the exhaust system.
  2. Seal any leaks found using exhaust repair tape or by replacing faulty sections of the pipe.

5. Reset the ECU

• Tools Required: OBD-II scanner
• After repairs are completed:
  1. Reconnect the negative battery terminal.
  2. Use an OBD-II scanner to clear the P0420 code from the ECU.
  3. Start the engine and let it idle for a few minutes to ensure the system is functioning correctly.