how to fix P0420 code on my Honda Accord Eleventh Generation (2023-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Sub-steps:
  1. Remove the upstream (pre-catalytic) oxygen sensor.
  2. Measure the voltage while the engine is running; it should fluctuate between 0.1V and 0.9V.
  3. If the readings are out of this range, replace the oxygen sensor.

3. Inspect Catalytic Converter

• Tools Required: Jack, jack stands, socket set
• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Inspect the catalytic converter for any physical damage or signs of overheating (discoloration).
  3. Check for any exhaust leaks before and after the catalytic converter.
  4. If the converter is damaged, remove it by unbolting it from the exhaust system.

4. Install New Components

• Tools Required: Socket set, torque wrench
• Sub-steps:
  1. If replacing the catalytic converter, install the new unit and torque the bolts to manufacturer specifications (typically around 30-40 ft-lbs).
  2. Reinstall the upstream oxygen sensor in the new catalytic converter.
  3. If replacement of the oxygen sensor was necessary, install the new sensor and torque it to specifications (typically 30-35 ft-lbs).

5. Reconnect Battery and Test

• Reconnect the battery and clear the error codes using the OBD-II scanner.
• Start the engine and let it idle for a few minutes.