said by mattmag:exactly, like i just posted, faulty cats threw that code on my both grand prix. same car as the impala, and those were the only codes i had said by Anonymous_:
If it was the catalytic converter I would be getting more codes besides the P0420
What makes you think that? Your assumption in this case is wrong. P0420 is very often a stand-alone code, and requires no other associated failures to enable it.