Thanks Timgco, you're a great help, if it cuts the fuel supply then I need to take it up with GM, not to mention getting hold of my copy of the manual.
Yesterday I travelled for around 120 miles (onroad and off) the light came on when I was offroad, and stayed on till I came back home. everything was fine except for that light that was always on.
This morning, I started the truck, everything was normal and the light was off
Thanks again
DuneH3