what does it mean if my Honda Accord has a check engine light with code P0420

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to avoid electrical shorts during repairs.

2. Inspect and Test Oxygen Sensors

• Sub-steps:
  • Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  • Disconnect the electrical connectors of both sensors.
  • Use a multimeter to check the resistance of the sensors according to manufacturer specifications.
  • If either sensor is faulty, replace it with a new part.
• Tools Required: Multimeter, socket set, O2 sensor socket.

3. Inspect Catalytic Converter

• Sub-steps:
  • Remove the exhaust heat shield if present to gain access to the catalytic converter.
  • Inspect the catalytic converter for physical damage or signs of overheating (e.g., discoloration).
  • Tap the converter lightly to check for internal rattling, which indicates internal failure.
  • If damaged, replace the catalytic converter with an OEM or equivalent part.
• Tools Required: Socket set, exhaust hanger removal tool.

4. Reassemble and Reconnect

• Sub-steps:
  • Reinstall any removed components, ensuring all bolts are torqued to manufacturer specifications.
  • Reconnect the oxygen sensors and battery.
  • Start the engine and allow it to reach operating temperature, checking for leaks.
• Tools Required: Torque wrench.