On a 98 vetteI heard removing the cat will cause the check engine light to remain lit, is this true?

Never heard that. I can't see why that would give you a check engine light

There are four O2's .. One in front of the cat on each side and one behind the cat on each side. The back are refered to as rear O2's. The O2's measure oxygen present in the exhaust gasses. By taking a reading in front of the cat and behind the cat the computer can compare oxygen levels and tell if a cat is working properly. The computer will set a cat low efficiency code if the cat is failed. If the cat is not present the rear O2 readings will be the same as the front O2 .. the computer thinks the cat is not burning off excess fuel / oxy passing so it will set a cat related code ... light on dash. The code can be "turned off" during a retune .. for off road use only .. :rolleyes: