same thing happened to me 2 weeks ago on my 99 Trooper (look at my post
down lower "Help w/ 99 Trooper"). I ended up taking it to dealer, he said
it was a TOD vacuum solenoid unit, something messed up with a sensor on
the front axle. It probably was not anything major, I am sure I could
have driven it like that for a while, but flashing really bugged me, so I
got it fixed. There went 200 bucks!