I find with my D40 - although not a 550 - i get this happening with longer beach stays. ill either be headed out of either a wet patch of sand or on the real powdery soft sand.
Everytime it happens the same lights come on and i put it down to the abs ( i think they are) sensor in the rear being wet ot sandy.
Heres what i would try first:
Does the car go into 4hi?
Don't need to be moving for this- have the car on and in neutral - spin the dial to change to 4x4 .. try 4lo?
Does it engage or does it flash?
The abs wires in the rear are on the inside of the chassis rails. The driver side one is just behind the top shock mount and the passenger side is in the similar place but on the round tube between either chassis rail.
you could start there and by unclipping these. Give them a couple of soft taps and maybe a hit of contact cleaner. while your there and have these unclipped, check for a broken wire.. they are thin little wires so best to take caution.
The front two are on the strut tower - wouldnt hurt to unplug these and a quick clean too..
If this is the issue, a car restart and a short drive will fix the issue
