Cooling Fans stay on after car is shut off

What is your question?

I've owned this car for over 10 years and really haven't had any major issues with it. However, last fall, the cooling fans began to stay on when I shut the car off and it didn't matter if the car was on 5 seconds or an hour. My mechanic said it was the onboard computer that was failing and the whole thing had to be replaced. He gave me an estimate of over $1000, which I choose not to replace becasue I thought I was going to sell the car. I've decided to keep the car now and want to make sure that I fix the right thing the first time around. Is this the fan controller or the complete onboard computer? Or is the controller part of the computer? Can anyone clarify this for me? Any help would be appreciated... Thanks!