2001 Durango engine service light

My 2001 durango has been an almost perfect vehicle for 95,000 miles. About 40,000 miles ago that dang engine light came on a stays on. Living in California I had my emissions checked and the trucks emissions were fine. The test facility mechanics even tried to reset the light to no avail.

Can anybody tell me how to reset it or do something to extinguish the dang thing?

RTT