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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to ensure safety during repairs.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench, penetrating oil.
• Steps:
  1. Locate the upstream and downstream oxygen sensors (typically near the exhaust manifold and after the catalytic converter).
  2. Apply penetrating oil to the sensor threads to ease removal.
  3. Disconnect the electrical connectors from both oxygen sensors.
  4. Use the O2 sensor socket to remove the sensors from the exhaust system.
  5. Install the new oxygen sensors by hand to avoid cross-threading, then tighten them to manufacturer specifications (usually around 30-40 lb-ft).
  6. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Jack and jack stands, socket set, exhaust gasket, torque wrench.
• Steps:
  1. Safely lift the vehicle using a jack and secure it with jack stands.
  2. Remove any heat shields or brackets securing the catalytic converter.
  3. Unbolt the catalytic converter from the exhaust system using the socket set (make sure to note the position of any gaskets).
  4. Inspect the exhaust manifold and the exhaust pipe for cracks or damage.
  5. Install the new catalytic converter, ensuring any gaskets are properly positioned.
  6. Torque the bolts to manufacturer specifications (check service manual for specific torque values).
  7. Reinstall heat shields or brackets as necessary.

4. Reset the ECU

• Tools Required: OBD-II scanner.
• Steps:
  1. Reconnect the vehicle battery.
  2. Use the OBD-II scanner to clear the P0420 code from the engine control unit (ECU).
  3. Start the engine and allow it to reach operating temperature.