The passenger side fan on my TJ takes forever to stop running once it starts running at idle. This is so bad that I have to remove the relay when I check ATF (fan blow fluid all over dipstick). When i pull into my garage at home, the fan won't be running, but after only a few seconds with the motor idling the passenger side cooling fan will cut in. I expected it to cut out after a minute or 2, but one can leave the car idling for 10 minutes and the fan keeps running. The temp gauge meanwhile stays at mid point. Switching aircon on and off makes no difference. If I rev the the car to about 3000rpm for about 2 minutes the fan will cut out but not for long, then it comes on again and stays on. On the TS that I had before, the fan would run only for a short time at idle and would cycle on and off and at the time it cut in, one could see the temp gauge was a little higher. I am concerned that the fan is running when not needed/too long/too often. I don't know what it is doing when I am stuck in traffic (fan probably running all the time, even when temp gauge has not moved). Any one have the same situation, any thoughts??

Shorted wiring, more likely to be temperature sensor.

Have you got your aircon on?
if so try with it off

Had the engine running with bonnet open on the weekend - the Right Hand (drivers side) thermo fan, was spinning away quite happily and the Left Hand (Passengers side) was not, until i turned the Airconidioning ON - then the Left Hand one came on / cycles in and out.

Turn the AC off - the left hand fan, stays off.

i think its coming on to help cool the trans fluid

All of my Magnas do the same as yours. Come on and stay on (Until I start moving that is). I just thought it was part of the computer control setup.