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

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery to avoid any electrical shorts.
• Raise the vehicle securely on jack stands.

2. Oxygen Sensor Inspection and Replacement

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  1. Locate the upstream O2 sensor near the exhaust manifold.
  2. Use the O2 sensor socket to unscrew and remove the sensor.
  3. Inspect the sensor for damage or contamination.
• Replace with a new OEM or high-quality aftermarket O2 sensor.
• Torque the new sensor to the manufacturer's specification (typically around 30 lb-ft).

3. Catalytic Converter Inspection

• Tools Required: Socket set, torque wrench
• Inspect the catalytic converter:
  1. Check for physical damage or signs of clogging.
  2. Look for discoloration or rattling noises when shaking the converter.
• If damaged, remove the catalytic converter:
  1. Disconnect any related exhaust hangers.
  2. Unbolt the catalytic converter from the exhaust pipe and exhaust manifold.
  3. Install a new catalytic converter, ensuring all gaskets are replaced and bolted to specifications.

4. System Reset and Final Checks

• Tools Required: OBD-II scanner
• Reconnect the battery.
• Clear the P0420 code using the OBD-II scanner.
• Start the engine and allow it to reach operating temperature.