Abs light stays on and four wheel light flashes

I just had this problem. If you notice some odd "clunking" when you brake as well, it's the ABS turning on. The problem is that there is a sensor ring near where the axle and wheel meet up called a "tone ring." They tend to crack on the Escapes. They cost about $7-$8 at Rock Auto (online, google for the address).
If you want to put it on yourself, it's a simple process...if you can get the bolts off the components.
Otherwise, don't let the dealer charge you the $500-$1000 they usually try to. Find a respectable mechanic, give them the replacement ring, and ask them to put it on. It should only take about a half hour at most with their tools.
Once the ring is replaced, it's smooth sailing.
Good luck!