Honda Civic 10th Generation (2016-2021) P0420 code meaning and how to fix it

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, jack and jack stands, safety goggles, gloves.
• Disconnect the battery to ensure safety while working on electrical components.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

• If oxygen sensor readings are faulty:
  1. Disconnect the electrical connectors from the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Use a wrench to remove the sensors from their respective locations.
  3. Install new oxygen sensors, ensuring they are properly torqued (typically 30 ft-lbs).
  4. Reconnect the electrical connectors.

3. Inspect and Replace the Catalytic Converter

• If the catalytic converter is determined to be inefficient:
  1. Use a wrench or socket set to remove the bolts securing the catalytic converter to the exhaust manifold and the exhaust pipe.
  2. Carefully lower the catalytic converter from the vehicle.
  3. Install the new catalytic converter, ensuring that it is aligned properly.
  4. Torque the bolts to the manufacturer’s specifications (usually 25-30 ft-lbs).

4. Reset the Engine Control Module (ECM)

• After repairs:
  1. Reconnect the battery.
  2. Use an OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and allow it to idle.