why does my Honda Pilot have a check engine light with code P0420

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool before starting work on the exhaust system.

2. Inspect and Replace Oxygen Sensors (if necessary)

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• If the oxygen sensors are faulty, follow these steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Unplug the electrical connectors from both sensors.
  3. Use the O2 sensor socket to remove the sensors from the exhaust system.
  4. Install new sensors by threading them into the exhaust system and tightening them to the manufacturer's specifications (typically around 30 lb-ft).
  5. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, wrench set, exhaust hanger removal tool.
• If the catalytic converter is damaged or clogged, replace it:
  1. Raise the vehicle securely using jack stands.
  2. Remove any heat shields covering the catalytic converter.
  3. Disconnect the exhaust pipe from the catalytic converter by loosening the flange bolts.
  4. Remove the catalytic converter from its mounting brackets and exhaust hangers.
  5. Install the new catalytic converter, ensuring all gaskets are in place and secure.
  6. Reconnect the exhaust pipe and tighten all bolts to the specified torque.