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

Solution

1. Preparation

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

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  1. Disconnect the electrical connector.
  2. Use the O2 sensor socket to remove the sensor.
• Install the new upstream oxygen sensor:
  1. Apply anti-seize compound to the threads (if applicable).
  2. Torque to manufacturer specifications (usually around 30 Nm).
• Repeat the same process for the downstream (post-catalytic converter) oxygen sensor if necessary.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool.
• Remove the catalytic converter:
  1. Loosen the bolts/nuts securing the catalytic converter to the exhaust manifold and the exhaust pipe.
  2. Remove exhaust hangers using the exhaust hanger removal tool.
• Install the new catalytic converter:
  1. Position the new converter and secure it with bolts/nuts.
  2. Torque to manufacturer specifications.
• Reconnect the exhaust hangers.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner.
• Reconnect the battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Take the vehicle for a test drive to ensure the engine operates normally and the code does not reappear.