how to fix P0420 catalyst efficiency below threshold in Honda Accord 9th Generation (2013-2017)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and securely raise it using jack stands.
• Disconnect the battery to ensure safety while working.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  2. Use the O2 sensor socket to remove the upstream sensor and inspect it for damage. Repeat for the downstream sensor.
  3. If damaged, replace with new sensors (ensure they are the correct part number for your vehicle).
  4. Torque the new sensors to the manufacturer's specifications (typically around 30 lb-ft).
  5. Reconnect the battery.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust gasket, penetrating oil
• Sub-steps:
  1. Remove the exhaust heat shield if applicable to access the catalytic converter.
  2. Apply penetrating oil to the bolts holding the catalytic converter in place and allow it to soak.
  3. Remove the bolts attaching the catalytic converter to the exhaust system using the socket set.
  4. Carefully detach the catalytic converter from the exhaust system and inspect for blockage or damage.
  5. If defective, install a new catalytic converter, ensuring to use a new gasket.
  6. Reattach the bolts and torque to manufacturer specifications (usually between 40-50 lb-ft).
  7. Replace the heat shield if removed.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner
• Sub-steps:
  1. Use the OBD-II scanner to clear any fault codes from the vehicle's computer.
  2. Start the engine and let it idle for a few minutes.
  3. Perform a test drive to ensure the vehicle operates correctly and recheck for any error codes.