I had the same problem, the o/d light can come on if your too low on fluid or its overheating and it will disable overdrive so you don't decimate your tranny. It always came on for me on the freeway or going up an incline, turned out i was super super low on tranny fluid like almost 3 quarts low. Ended up having a leak and having to replace rear main seal, transfer case seal, and drain plug seal. Also sometimes itll throw that code about the pressure sensor or overdrive solenoid about it shorting. Its shorting cause it doesnt have enough fluid.