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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  • Locate the sensor on the exhaust manifold.
  • Use the O2 sensor socket and ratchet to unscrew the sensor.
• Check the sensor for carbon buildup or damage, and replace if necessary.
• Install the new sensor:
  • Apply anti-seize compound to the threads (if applicable).
  • Torque to manufacturer specifications (typically around 30 lb-ft).
• Repeat the same process for the downstream (post-catalytic converter) oxygen sensor if needed.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if necessary), torque wrench.
• Inspect the catalytic converter for any physical damage:
  • Look for dents, cracks, or signs of melting.
• If replacement is necessary:
  • Raise the vehicle and secure it with jack stands.
  • Cut the exhaust pipes before and after the catalytic converter if necessary using an exhaust pipe cutter.
  • Remove the old catalytic converter.
  • Install the new catalytic converter:
    • Ensure proper alignment with exhaust pipes.
    • Use new gaskets as needed.
    • Torque bolts to manufacturer specifications.
• Reconnect any O2 sensors previously removed.

4. Clear Codes and Test

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Start the engine and let it run for a few minutes while checking for leaks.
• Perform a test drive to ensure the check engine light does not reappear.