how to diagnose a P0420 code in my Honda Pilot Third Generation (2016-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle battery to ensure safety.
• Allow the engine to cool down before proceeding.

2. Oxygen Sensor Testing

• Tools Needed: OBD-II scanner, multimeter.
• Sub-steps:
  1. Reconnect the battery and start the engine.
  2. Use the OBD-II scanner to read live data from both the upstream and downstream oxygen sensors.
  3. Check that the upstream sensor fluctuates between 0.1V and 0.9V while the engine is running, indicating proper operation.
  4. If the upstream sensor is functioning correctly, proceed to test the downstream sensor.

3. Inspect and Replace Oxygen Sensors (if necessary)

• Tools Needed: Oxygen sensor socket, wrench set, penetrating oil.
• Sub-steps:
  1. If the downstream sensor shows a steady voltage (not fluctuating), carefully remove it using an oxygen sensor socket.
  2. Apply penetrating oil to the threads if necessary, and allow it to soak for a few minutes.
  3. Install the new oxygen sensor following the manufacturer’s torque specifications (typically around 30 lb-ft).
  4. Reconnect the battery and clear the error codes.

4. Catalytic Converter Inspection and Replacement (if necessary)

• Tools Needed: Socket set, torque wrench, exhaust gasket.
• Sub-steps:
  1. If the catalytic converter is damaged or clogged, remove the exhaust pipes connected to it using the socket set.
  2. Inspect the catalytic converter for physical damage or excessive heat.
  3. Replace the catalytic converter with a new unit, ensuring that all gaskets are replaced as well.
  4. Reinstall the exhaust pipes and tighten all fasteners to the manufacturer’s torque specifications.