what kinda of car we talking here?

if its a 3800, it could be the temp sensor under the t stat. its got two parts, one to the pcm, one to the dash. if its shot to the pcm it may just make the fans come on full time as a safety.

or its harness is shot. when you unplug the temp sensor the fans will run full time. the harness bakes in the heat inches off the crossover pipe.

if you have a torque app see what it says your temp is. if it dont show a temp that could be the harness or sensor.