97 cat problem

I have friend with a 97 taurus. The check engine light came on so he brought it to the dealer. They said is catalytic converter is bad and needs to be replaced.

Is there anyway to verify the dealers diag on the cat? Did they just read an error code, or is there a telltail sign they look for?

They also said a bad cat will ruin the engine. Anyone know how?

Thanks,
jim

Usually the sign of a bad cat is the operating tempature of it..If you want to verify the dealers results you can go to another dealer and ask them to pull the code and see what it means...It can cause engine problems too..