how to fix P0420 code on Honda Accord 8th Generation (2008-2012)

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, infrared thermometer, safety glasses, gloves.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical issues during repairs.

2. Inspect and Repair Exhaust Leaks

• Sub-steps:
  1. Visually inspect the exhaust system for leaks, particularly at joints and connections.
  2. Use an exhaust leak detection spray or soap solution to locate small leaks.
  3. If leaks are found, repair or replace damaged components (e.g., gaskets, pipes).

3. Test and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic converter) and downstream (post-catalytic converter) oxygen sensors.
  2. Use the OBD-II scanner to monitor sensor outputs while the engine is running.
  3. If the sensors are not functioning within specifications (typically 0.1 to 0.9 volts for switching), replace them with OEM or quality aftermarket parts.
  4. Torque new sensors to manufacturer specifications (usually around 30-40 lb-ft).

4. Catalytic Converter Inspection and Replacement

• Sub-steps:
  1. If the catalytic converter is suspected to be clogged, remove it from the exhaust system.
  2. Inspect the substrate for melting or blockage. If defective, replace with a new catalytic converter.
  3. Ensure all mounting hardware is in good condition and replace if necessary.
  4. Reinstall the catalytic converter and torque bolts to manufacturer specifications (typically around 30 lb-ft).

5. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the negative battery terminal.
  2. Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.
  3. Take the vehicle for a test drive to ensure the issue is resolved and monitor for any reoccurrence of the check engine light.