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

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, jack and jack stands, safety glasses, gloves.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the battery to avoid any electrical issues.

2. Inspect and Test O2 Sensors

• Sub-steps:
  1. Locate the upstream (Sensor 1) and downstream (Sensor 2) O2 sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use a multimeter to test the resistance of both sensors. Replace any sensor that is out of specifications.
  4. Reconnect the sensors and clear the P0420 code using the OBD-II scanner.

3. Inspect the Catalytic Converter

• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Visually inspect the catalytic converter for any physical damage or signs of overheating (discoloration, cracks).
  3. Tap gently on the converter; if you hear a rattling noise, it may be internally damaged.
  4. If damaged, proceed to replace the catalytic converter.

4. Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. Remove the exhaust pipe bolts securing the catalytic converter using a socket set.
  2. Disconnect any brackets or hangers that may be holding the converter in place.
  3. Remove the old catalytic converter and replace it with a new one, ensuring a proper seal.
  4. Tighten all bolts to the manufacturer's specified torque settings.
  5. Reconnect any electrical connectors previously disconnected.

5. Reassemble and Test

• Sub-steps:
  1. Lower the vehicle back to the ground.
  2. Reconnect the battery.
  3. Start the engine and allow it to reach operating temperature.
  4. Use the OBD-II scanner to ensure the P0420 code has not returned.