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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, multimeter
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors in the exhaust system.
  2. Disconnect the electrical connectors of the sensors.
  3. Use the O2 sensor socket to remove the old sensors.
  4. Install the new sensors by threading them in and tightening to the manufacturer's torque specifications (typically 30-40 ft-lbs).
  5. Reconnect the electrical connectors securely.

3. Inspect and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, wrench set, exhaust hanger removal tool
• Sub-steps:
  1. Inspect the catalytic converter for physical damage or rattling.
  2. If replacement is needed, remove the exhaust hangers using the exhaust hanger removal tool.
  3. Unbolt the catalytic converter from the exhaust manifold and the exhaust pipe.
  4. Install the new catalytic converter, ensuring to use new gaskets if required.
  5. Bolt the converter in place, tightening to the manufacturer's torque specifications (typically 20-30 ft-lbs).
  6. Reattach exhaust hangers to secure the exhaust system.

4. Reset the Engine Control Module (ECM)

• Tools Required: OBD-II scanner
• Sub-steps:
  1. Reconnect the battery after completing repairs.
  2. Use the OBD-II scanner to clear the P0420 code from the ECM.
  3. Perform a test drive to ensure the code does not return.