my check engine light came on yesterday. we plugged it in and got the code P0420 (catyalist system efficiency below threshold bank 1) we were told its probly the catalytic converter but the whole exahust system was replced 2 years ago. could it be an o2 sensor? or could there be something else wrong that would cause the cat. conv. to go bad so fast again? please help . thanks!

 

Year of car? California or Federal emissions?

The converter should have a warranty, check paperwork.

Typically if this code alone then converter is the issue.

Depending on year of car it may be possible to have data taken from the computer to determine if the sensors are functioning OK. And confirm they are generating the signal for a failed converter.

 

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1)