How do I fix my P0420 code?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

The p0420 code is a code for a catalytic converter efficiency below threshold. There are a few reasons why this might happen, but the most common reason is that the catalytic converter is not working properly. This can be caused by a variety of things, such as a clogged converter, a damaged converter, or a problem with the oxygen sensor.

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1. Check engine light and code reader for specific trouble codes

  1. Turn the car off and then on again
  2. check the dash lights
  3. check the engine light
  4. if the engine light is on, go to step 5
  5. if the code reader doesn't detect the code, go to step 6
  6. turn off the car and then back on
  7. check the dash lights
  8. if the code reader detects the code, go to step 9
  9. if the code reader doesn't detect the code, turn off the car and then back on
  10. check the engine light
  11. if the engine light is off, the code reader may not have detected the code, go to step 12
  12. if the engine light is on, the code reader may have detected the code, and the car needs to be brought in for repair, go to step 13

2. Inspect the exhaust system for leaks

First, start by looking for any signs of leaking fluids, such as oil or coolant seeping from the engine or exhaust system. If you see any signs of fluid leakage, start by checking the engine oil level and the coolant level. If the levels are correct, then it's likely that the leak is coming from another part of the car. Next, inspect the exhaust system for any signs of damage. If you find any signs of damage, it's likely that the leak is coming from the exhaust system. If the system is damaged, it may be difficult to fix the leak. If the exhaust system is leaking, you may need to replace the exhaust system.

3. Check the oxygen sensor and replace if necessary

  1. Open the hood and allow the engine to cool.
  2. Remove the air filter.
  3. Remove the plastic cover over the oxygen sensor.
  4. Remove the sensor.
  5. Replace the sensor with a new one.
  6. Replace the cover over the sensor.
  7. Replace the air filter.
  8. Close the hood.
  9. Start the engine and check the O2 sensor readings.

If the answers above didn't work then you should also try:

  1. Check the air filter and replace if necessary.
  2. Check the fuel system for leaks and repair if necessary.
  3. Have the vehicle's computer system checked for codes.