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

Solution

1. Preparation

• Gather tools and parts for the repair.
• Disconnect the battery to ensure safety while working with electrical components.

2. Inspect and Replace Oxygen Sensors

1. Tools Required: O2 sensor socket, ratchet, torque wrench.
2. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
3. Remove the upstream oxygen sensor:
   • Use the O2 sensor socket to unscrew it from the exhaust manifold.
   • Disconnect the electrical connector.
4. Install the new upstream oxygen sensor:
   • Apply anti-seize compound to the threads of the new sensor.
   • Torque to manufacturer specifications (typically around 30-35 ft-lbs).
5. Repeat the process for the downstream oxygen sensor.

3. Replace Catalytic Converter (if necessary)

1. Tools Required: Socket set, penetrating oil, torque wrench.
2. Remove the exhaust system components connected to the catalytic converter (if applicable):
   • Use penetrating oil on rusted bolts for easier removal.
   • Remove any hangers or brackets securing the exhaust.
3. Remove the catalytic converter:
   • Unscrew the bolts or nuts securing it to the exhaust manifold and the exhaust pipe.
   • Carefully take out the old catalytic converter.
4. Install the new catalytic converter:
   • Position it correctly and secure it using new gaskets if required.
   • Torque all bolts to manufacturer specifications.
5. Reconnect any exhaust components that were disconnected.

4. Clear Codes and Test

1. Reconnect the battery.
2. Use the OBD-II scanner to clear the P0420 code.
3. Start the engine and allow it to warm up.
4. Take the vehicle for a test drive to ensure the check engine light does not return.