I agree as with some above and from my experience having a 2005 escape, that its one of your wheel speed sensor "tone" rings! the issue for me was the exact same warnings "service four wheel drive" alternate with "service brake system" I had it looked at and fixed by an ex ford mechanic workmate whom is now a millwright and has a shop at home and does mechanics on the side, and sure enough the ring on right passenger side was split causing it to move away slightly from its normal position, he told me that apparently these rings are made extremely thin and over time rust forms underneath from moisture, expands and finally splits the ring! in my simple layman's understanding its the wheel speed sensors that determine which wheels are spinning at which rate, if for example both front wheels stopped rotating and back ones still turning then vehicle realizes its in a skid and the abs is activated. same with the auto four wheel drive if various wheel slippage is detected then that system is engaged! my neighbor has the same vehicle and experienced the same warning problem within a couple of months of mine! the replacement part was surprisingly inexpensive with this new found knowledge of what his problem was I was able to help him replace his in his carport with the aide of a Haynes manual as a guide and of course a little more time taken than it would of a more experienced mechanic! :)