Northwoods Snowman

OK, no luck searching around. I've noticed this winter that when I put my XJ in 4x4 and I get the ABS to kick on when hitting the brakes, the ABS will work for that stop, but then it turns on the light and shuts the system off. Doesn't do it in 2x4 so I'm thinking that it is freaking out because it can't modulate the front and rear separately and just shuts off. Any ideas what might be causing this? I don't want to spend $$$ at the dealer to have them check for a code only to find out nothing is there. After I cycle the ignition off and then back on it usually resets and turns the light off, thought the last time or two (I've been gone for a month for work) I think I had to turn it off a couple times. Eventually though the light always goes out, and only seems to turn on when in 4x4. Any thoughts?

The only thing I can think of is maybe the G-sensor? But I have no idea how to test it and my manual doesn't tell me anything either.