Cadillac Repair: 98 cadillac deville, blown head gaskets, radiator cap

Question
I install new water pump, new thermostat and water resovior
for radiator but still overheat goes above 251 degree I used the OBD2 to scan for code but it shows PO44O, PO741, and P1258 what does it mean could you explain please?

Answer
This engine is very very common to developing blown head gaskets in numerous areas of the head gasket without showing the tell tale signs of white smoke from the exhaust.

What happens is that the combustion chamber pressure builds up within the cooling system and prevents the cooling system from allowing normal coolant flow.

You need to have the head gaskets tested via putting constant air pressure into each spark plug hole and look for bubbles in the radiator cap opening.