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

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, safety glasses, gloves.
• Safety Warnings: Disconnect the battery before working on electrical systems; allow the engine to cool before inspecting the exhaust.

2. Inspect and Replace Oxygen Sensors

• Remove the negative battery terminal.
• Locate the upstream and downstream oxygen sensors (usually found in the exhaust manifold and after the catalytic converter).
• Unplug the electrical connectors from both oxygen sensors.
• Use a socket wrench to remove the sensors from the exhaust system.
• Install new oxygen sensors by threading them into their respective positions and tightening them to the recommended torque (typically 30-40 lb-ft).
• Reconnect the electrical connectors securely.

3. Inspect and Replace Catalytic Converter

• Inspect the catalytic converter visually for damage or excessive buildup.
• If replacement is necessary:
  • Remove any heat shields that may be obstructing access using a socket set.
  • Unbolt the catalytic converter from the exhaust system using appropriate socket sizes.
  • Install the new catalytic converter in reverse order, ensuring all gaskets are replaced and connections are secure (tighten bolts to manufacturer specifications).

4. Reset the ECU

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 trouble code from the vehicle's ECU.