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

Solution

1. Preparation

• Gather all tools and parts required for the repair.
• Ensure the vehicle is parked on a flat surface with the engine off and cool.
• Disconnect the negative battery terminal to prevent any electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream oxygen sensor:
   • Locate the upstream oxygen sensor in the exhaust manifold.
   • Use an O2 sensor socket to unscrew it.
   • Disconnect the electrical connector.
2. Install the new upstream oxygen sensor:
   • Apply anti-seize compound to the threads of the new sensor.
   • Screw it into the manifold and tighten to the manufacturer's specifications (usually around 30-40 ft-lbs).
   • Reconnect the electrical connector.
3. Repeat for the downstream oxygen sensor located near the catalytic converter using the same procedure.

3. Inspect and Replace the Catalytic Converter

1. Remove the catalytic converter:
   • Lift the vehicle and support it on jack stands.
   • Unbolt the catalytic converter from the exhaust system using a socket set (typically 14-17 mm bolts).
   • Carefully detach the converter from the exhaust pipe.
2. Install a new catalytic converter:
   • Position the new catalytic converter and secure it with bolts.
   • Ensure all gaskets are in place and use new gaskets if necessary.
   • Torque the bolts to the manufacturer's specifications (check specific values for your model).
3. Reconnect the exhaust system:
   • Reattach any hangers or brackets that were removed.

4. Clear the Codes and Test

1. Reconnect the battery and start the engine.
2. Use an OBD-II scanner to clear the P0420 code from the system.
3. Take the vehicle for a test drive to ensure the check engine light does not reappear.