an engine overheat will cause a cel if it is bad enough. the water pump may be a cause; could also be a stuck thermostat. When the engine overheats, do you still get warm air out of the vents? if not, suspect the water pump. if neither of those cure the problem, you might have a plugged up radiator. when you're replacing the water pump and thermostat, check it for any other coolant leaks and repair those..
