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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream (pre-catalytic) oxygen sensor:
   • Use an O2 sensor socket to unscrew the sensor.
   • Disconnect the wiring harness.
2. Install the new upstream O2 sensor:
   • Apply anti-seize compound on the threads of the new sensor.
   • Screw it in by hand, then tighten to the manufacturer's specifications (typically around 30 lb-ft).
3. Repeat for the downstream (post-catalytic) oxygen sensor if necessary.

3. Inspect and Replace the Catalytic Converter

1. Lift the vehicle safely:
   • Use jack stands to support the vehicle securely.
2. Remove the exhaust pipe connected to the catalytic converter:
   • Use a socket set to unbolt the flange connection.
   • Disconnect any hangers or brackets securing the exhaust.
3. Remove the catalytic converter:
   • Unbolt it from the exhaust manifold and exhaust pipe.
   • Carefully detach it from the vehicle.
4. Install the new catalytic converter:
   • Position the new converter and secure it with bolts to the exhaust manifold and pipe.
   • Ensure proper alignment and tighten bolts to the specified torque.
5. Reattach the exhaust pipe and secure all hangers.

4. Reconnect Battery and Clear Codes

1. Reconnect the negative battery terminal.
2. Use an OBD-II scanner to clear the P0420 code from the ECM.

5. Test Drive

• Take the vehicle for a test drive to ensure the check engine light does not return and that performance is restored.