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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Ensure the vehicle is on a level surface and secure with jack stands.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream oxygen sensor:

   • Locate the upstream (pre-catalytic converter) oxygen sensor.
   • Use an oxygen sensor socket to unscrew it from the exhaust manifold.
   • Disconnect the sensor's electrical connector.

2. Install the new upstream oxygen sensor:

   • Apply anti-seize compound to the threads of the new sensor.
   • Screw it into place and tighten it to manufacturer specifications (usually about 30 lb-ft).
   • Reconnect the electrical connector.

3. Remove the downstream oxygen sensor:

   • Locate the downstream (post-catalytic converter) oxygen sensor.
   • Use the oxygen sensor socket to unscrew it from the exhaust pipe.
   • Disconnect the sensor's electrical connector.

4. Install the new downstream oxygen sensor:

   • Apply anti-seize compound to the threads of the new sensor.
   • Screw it into place and tighten it to manufacturer specifications.
   • Reconnect the electrical connector.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Check catalytic converter condition:
   • If previous steps do not resolve the issue, inspect the catalytic converter for physical damage or blockage.
2. Remove the catalytic converter:
   • Unbolt the catalytic converter from the exhaust system. Use a socket set and follow the manufacturer’s torque specifications.
   • Use penetrating oil if bolts are rusted.
3. Install the new catalytic converter:
   • Position the new catalytic converter and secure it using new gaskets and bolts.
   • Torque the bolts to manufacturer specifications.
4. Reconnect any exhaust hangers.

4. Reconnect Battery and Clear Codes

• Reconnect the battery terminals.
• Use an OBD-II scanner to clear the stored P0420 code.
• Start the engine and allow it to reach operating temperature.