Catalytic converter?

I have a 1999 Chevy Lummina that the converter goes out every once a year for the past three years


The mechanic does a test with his computer tester.


I have taken it to different repair shops and they all tell me the same thing.


I have just over 70,000 miles on it.


That has been the only mechanical problem it has ever had.





What could be the problem ?|||If you don't use it much, and you have it park outside. they buildup rust faster from humidity..OR take it OFF if you don't have state inpections.Bye universal converters, cost less.try a better gas station...gasoline might be bad.Might be burning too rich too...|||hey maybe it should have two. if its missing one your making the one that is there work to hard. My car has 4 catalytic converters.