99 deville; can the code p0440 be relative to a bad catalytic converter

Question

My car is overheating still after I replaced water pump, thermostat and cap. There are no leaks and I'm thinking the converter is clogged and causing air build up in the block.

Answer 1

P0440 Evaporative emission control system malfucntion

This code is not related to the catalytic convertor. If you have a build up of air in the block, what you have is combustion entering into the cooling system.

 Here is headgasket that failed, where it sealing failed and allowed combustion to enter into the cooling port. The only fix here was to perfrom a headgasket.