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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Remove the electrical connectors from both sensors.
3. Using an O2 sensor socket, unscrew both sensors from the exhaust pipe.
4. Install the new oxygen sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Torque to manufacturer's specifications (usually around 30 ft-lbs).
5. Reconnect the electrical connectors to both sensors.

3. Inspect and Replace Catalytic Converter

1. Remove any heat shields or components obstructing access to the catalytic converter.
2. Unbolt the catalytic converter from the exhaust system using a socket set.
3. Inspect the old catalytic converter for signs of damage or clogging.
4. Install the new catalytic converter:
   • Ensure proper alignment with the exhaust system.
   • Torque bolts to manufacturer specifications.
5. Reattach any heat shields or components removed during disassembly.

4. Reset the Engine Control Module (ECM)

1. Reconnect the negative battery terminal.
2. Use an OBD-II scanner to clear the P0420 code from the ECM.
3. Start the engine and let it idle for a few minutes.