forester 1998- malfunction code p0438 on a

I have a question, if anybody can help; what should I target to replace when the malfunction code P0483-Cooling Fan Rationality Check Malfunction is on.
any help will be appreciated.
forester 1998

turn the a/c on and make sure the fans come on.this is just to check if they do work.the coolant sensor is almost always the fault but there can be others that i would help you with.first check these and also when engine is hot check the temperature of both the upper and lower radiator hoses.they should be the same temp if system working correctly.caution hoses will be hot for some people to touch.