Only the Hill Decent Control light is illuminated? The only reason that would come on by itself would be because you pushed the button. Otherwise you will have the three amigos which indicates an ABS system fault. Either way, it doesn't really matter.
Not the green active DHC light, but the orange/amber warning DHC light.
On my 03, the DHC button is to the right of the steering wheel by AC.
Also, we went to eat right after the light came on, when I restarted it a while later, all 3 Amigos were on. 1st time in 7500 miles and first since I did the circuit ground jump mod. When I got to the hotel, I restarted it twice. DHC warning light came on the first time. Second time no warning lights at all.
About 2 hours before the DHC warning light came on, we hit some standing water on I-15 causing a tense moment of hydro planing, and the ABS system kicked in for a brief moment. So maybe that has something to do with it.