how to fix Honda Civic 10th Generation (2016-2021) P0420 code

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shock.

2. Inspect and Replace Oxygen Sensors

1. Locate the Oxygen Sensors: Find the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
2. Remove the Upstream Oxygen Sensor:
   • Use an oxygen sensor socket and ratchet to unscrew the sensor.
   • Disconnect the electrical connector.
3. Remove the Downstream Oxygen Sensor:
   • Repeat the process for the downstream sensor.
4. Install New Oxygen Sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Install the upstream sensor first, followed by the downstream sensor, and tighten to the manufacturer's torque specifications (usually around 30-35 lb-ft).
5. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Inspect the Catalytic Converter:
   • Check for signs of physical damage, such as dents or holes, and ensure it is not clogged.
2. Remove the Catalytic Converter:
   • Loosen the exhaust flange bolts and remove the mounting brackets.
   • Disconnect any oxygen sensors attached to the converter.
3. Install New Catalytic Converter:
   • Position the new catalytic converter and secure it using new gaskets.
   • Tighten the bolts to the specified torque (typically around 30-40 lb-ft).
4. Reconnect all components, including oxygen sensors.

4. Reset Engine Control Module (ECM)

1. Reconnect the Battery: Reconnect the battery terminals securely.
2. Clear the Error Codes: Use the OBD-II scanner to clear the P0420 code from the ECM.