Which fan? there are 4.
The 2001 Rubicon is FULL time 4x4 from factory. Unless you installed a 2x4/4x4 select then it should always be in 4wheel drive.
Which fan are you refering too? cooling fanHeater fan
fan motor could be bad
2003
i'm assuming you mean your computer processor fan. If so, replace it. It's dead!
When you say "cooling fan", do you mean the radiator fan or the cabin air fan? If the radiator fan and the compressor are failing to come on, it could just be low refrigerant but in either case there is no guarantee that any single component would cause what you describe. It could be a fuse, relay, controls, connector or any of a number of possible causes.
2003
Maybe of your talking on a fan site it will take him awhile
check fan relay, fuses. jump power to fan. check freon level in a/c system.
no he wont he madyes...but he wait until 15.000 fan invite him!
It could be as simple as a fan relay. Check those first.