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

Solution

1. Preparation

• Gather required tools and parts.
• Ensure the vehicle is on a level surface and the engine is cool.
• Disconnect the battery.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  1. Locate the upstream O2 sensor.
  2. Use an O2 sensor socket to unscrew and remove it.
  3. Install the new sensor and torque it to manufacturer specifications (typically around 30 lb-ft).
• Repeat the process for the downstream (post-catalytic converter) oxygen sensor if it's also faulty.

3. Check and Replace the Catalytic Converter (if needed)

• Tools Required: Socket set, torque wrench, gasket scraper
• Remove the catalytic converter:
  1. Disconnect the exhaust pipes from the catalytic converter by removing the bolts.
  2. If necessary, remove any heat shields or brackets.
  3. Carefully detach the catalytic converter from its mounts.
• Install the new catalytic converter:
  1. Position the new catalytic converter in place and secure it with bolts, torquing them to manufacturer specifications.
  2. Reinstall heat shields or brackets if removed.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner
• Reconnect the battery.
• Use an OBD-II scanner to clear the P0420 code.
• Test drive the vehicle to ensure the check engine light does not reappear.