How do you fix a P0420 code?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

The p0420 code is a generic code that indicates that the catalytic converter on the vehicle is not functioning properly. There are a number of reasons why this code could be triggered, including a clogged converter, a faulty oxygen sensor, or a problem with the engine's fuel mixture. In most cases, a mechanic will need to diagnose the problem in order to determine the best course of action.

You are here because you have a question about:

  • error code 420
  • error code po420
  • catalytic converter error code
  • p0420

1. Check the engine for leaks

  1. Remove the engine cover. Refer to Engine Cover Replacement - C6 Corvette.
  2. Locate the engine oil cooler. Refer to Engine Oil Cooler - C6 Corvette.
  3. Remove the engine oil cooler hose and check for leaks. Refer to Engine Oil Cooler - C6 Corvette.
  4. Check for leaks around the engine oil filler cap and around the engine oil drain plug. Refer to Engine Oil - C6 Corvette.
  5. If necessary, replace the engine oil cooler hose. Refer to Engine Oil Cooler - C6 Corvette.

2. Check the exhaust system for leaks

  1. Park the car in a safe area and turn the engine off.
  2. Inspect the exhaust system for any obvious leaks. If there are any, use a sealant or patch to fix them.
  3. Reattach the exhaust system to the car.
  4. Turn the engine on and listen for any leaks. If there are any, fix them and drive the car.

3. Check the oxygen sensor

  1. Disconnect the negative battery cable.
  2. Remove the airbag sensor.
  3. Remove the front airbag.
  4. Remove the upper airbag module.
  5. Remove the oxygen sensor.
  6. Clean the area around the sensor.
  7. Reinstall the sensor.
  8. Reconnect the electrical connectors.
  9. Reconnect the negative battery cable.

4. Check the catalytic converter

  1. Remove the hood and front bumper.
  2. Remove the four bolts securing the catalytic converter to the exhaust system.
  3. Move the converter to the side and remove it.
  4. Check the converter for cracks, tears, or other damage. If it's damaged, replace it.
  5. Clean the inside of the converter with a brush and solvent.
  6. Coat the converter with a new sealant.
  7. Replace the bolts, washers, and nuts.

5. Reset the computer

  1. Enter the manufacturer's setup utility
  2. Select the "reset" tab
  3. Select "advanced options"
  4. Select "memory"
  5. Delete all of the memory from the computer
  6. Reinstall the operating system
  7. Restore the factory settings
  8. Reinstall the software that caused the problem