how to fix Honda Accord 10th Generation (2018-2022) P0420 code

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before working on exhaust components.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter.
• Sub-steps:
  1. Use the OBD-II scanner to clear the P0420 code and test drive the vehicle to see if the code reappears.
  2. If the code returns, use the multimeter to check the voltage output of the upstream oxygen sensor while the engine is running. The voltage should fluctuate between 0.1 to 0.9 volts.
  3. Repeat the test for the downstream oxygen sensor; it should show a stable voltage around 0.5 volts if the catalytic converter is functioning correctly. If either sensor is faulty, replace it.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust pipe cutter (if needed).
• Sub-steps:
  1. If the oxygen sensors are functioning correctly, visually inspect the catalytic converter for any signs of damage or blockage.
  2. If damaged, remove the exhaust pipes connected to the catalytic converter using a socket set.
  3. If applicable, use an exhaust pipe cutter to remove the old catalytic converter if it's welded in place.
  4. Install the new catalytic converter, ensuring it is oriented correctly.
  5. Use a torque wrench to tighten the bolts to the manufacturer's specifications (typically 25-30 ft-lbs).
  6. Reconnect the exhaust system and ensure all connections are secure.