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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, exhaust temperature gauge.
• Ensure the vehicle is parked on a flat surface, and the engine is off and cool.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Disconnect the negative battery terminal to ensure safety.
  2. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  3. Remove the connectors from both oxygen sensors.
  4. Use a socket wrench to unscrew and remove the sensors.
  5. Install the new oxygen sensors in reverse order, ensuring they are correctly torqued according to manufacturer specifications (typically around 30 ft-lbs).
  6. Reconnect the battery terminal.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. If the P0420 code persists after replacing the oxygen sensors, further inspect the catalytic converter for damage.
  2. Remove the exhaust system components leading to the catalytic converter (may require a socket set).
  3. Unbolt the catalytic converter from the exhaust manifold and exhaust pipe.
  4. Install the new catalytic converter, ensuring all gaskets are replaced.
  5. Torque all bolts to manufacturer specifications (check for specific torque values).
  6. Reassemble any removed exhaust components.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Use the OBD-II scanner to clear the P0420 trouble code.
  2. Start the engine and let it idle, then take the vehicle for a test drive to ensure proper operation and check for any reoccurrence of the code.