Causes for converter turning on check engine light

[sidnau]

My 2003 Corolla-Matrix (basic engine) has turned on the check engine light because the catalytic converter is not performing according to specifications. I would like to find out if there is some engine problem that has caused this to happen. The car has 160,000 miles, has been maintained well, and runs well. I have needed to add coolant 5-10 times since the car was new and the dealer seems to think this loss of coolant is not a cause for concern. (The dealer has not checked for coolant leaks or checked for the possibility of burning coolant.) Has anyone had a Corolla converter start failing, and was a cause found? (Of course, the converter could just be wearing out, but by the book, that shouldn't happen). Thanks.

[TrdSpeed140]

maybe it's the coolant that you might be burning that's fouling up the cat?

[mikered30]

Do you have any deposits on your oil cap?

[toyomoho]

If the coolant is being vaporized and flowing through the converter it will poison it.