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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before starting any work on the exhaust system.

2. Inspect and Replace O2 Sensors (if necessary)

• Tools Required: O2 sensor socket, wrench, penetrating oil.
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Apply penetrating oil to the sensor threads and wait a few minutes.
  3. Disconnect the electrical connectors from both sensors.
  4. Use the O2 sensor socket to unscrew the sensors from the exhaust system.
  5. Install new sensors by screwing them in and connecting the electrical plugs. Ensure they are tightened to manufacturer specifications (typically around 30 ft-lbs).

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket.
• Sub-steps:
  1. Raise the vehicle securely on jack stands.
  2. Remove the bolts securing the catalytic converter to the exhaust manifold and the exhaust pipe.
  3. Carefully remove the old catalytic converter from the vehicle.
  4. Install the new catalytic converter, ensuring the exhaust gaskets are in place.
  5. Tighten the bolts to the manufacturer's torque specifications (usually around 30-35 ft-lbs for exhaust connections).

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner.
• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and allow it to reach normal operating temperature.
  4. Take the vehicle for a test drive to ensure the issue is resolved and monitor for any reoccurrence of the code.