Friend has a over heating problem in his Altima. He took it to a Nissan Dealer and found that the fans do not turn on. Thermostat was replaced, Temp Control Valve, etc. They told him that the problem is in the computer. Make any sense?

They then advised him to buy an aftermarket fan and bypass the computer so that the fan turns on at the proper time. Is this possible, if so, How?

I have no clue, this is what he told me.

Any advice is welcome.

Thanks in advance