The Eco light comes on when you are driving economically, like coasting or traveling at a steady speed. It has nothing to do with MDS other than MDS tends to come on when you are driving at a steady speed or coasting. I use it to 'learn' how to keep my foot out of the pedal when Im running low on cash. I keep having a warning light of a giant gas pump appear on my dash every couple of days. Wish that one would go away.