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

Solution

1. Preparation

• Gather tools and parts necessary for the repair.
• Disconnect the negative battery terminal to prevent any electrical shorts.
• Allow the engine to cool completely before starting work.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream oxygen sensor:
   • Use an oxygen sensor socket to carefully unscrew the sensor from the exhaust manifold.
   • Disconnect the electrical connector.
2. Install the new upstream oxygen sensor:
   • Apply anti-seize compound to the threads of the new sensor.
   • Screw the new sensor into the manifold and tighten to the manufacturer's specification (usually around 30 lb-ft).
   • Reconnect the electrical connector.
3. Repeat for the downstream oxygen sensor if necessary, following the same steps as above.

3. Inspect and Replace the Catalytic Converter

1. Remove the exhaust system components:
   • If required, unbolt the flange connections and any hangers securing the exhaust system before the catalytic converter.
   • Use penetrating oil if bolts are rusted.
2. Inspect the catalytic converter:
   • Check for any signs of physical damage or blockage.
3. Install the new catalytic converter:
   • Position the new catalytic converter and secure it with new gaskets and bolts.
   • Torque the bolts to the manufacturer’s specifications.
4. Reassemble the exhaust system:
   • Reattach any removed components, ensuring all connections are tight and secure.

4. Clear Codes and Test Drive

1. Reconnect the battery:
   • Reattach the negative battery terminal.
2. Clear the P0420 code:
   • Use the OBD-II scanner to clear the code from the ECU.
3. Perform a test drive:
   • Drive the vehicle under various conditions to ensure that the check engine light does not reappear and that the car operates normally.