Go into settings > location and make sure that both gps wifi and gps satellite are checked. Hope that helps. - sheureka

 

Original Transformer or the Prime?
(Prime has serious GPS issues. So much that Asus stopped advertising that it comes with GPS.)

I would try turning GPS on, restart the tablet.

If it doesn't work in the car, go outside (away from buildings, so you can see like 7/8 of the sky) and try to pull up maps or whatever.

 

So it's only working on wifi? Turn off wifi, and make sure your gps satellite is checked on the tablet. The wifi for some reason is overriding the gps signal. I'd then try turning wifi back on once you get a decent signal. Good luck! - sheureka