After a search on the subject I'm still puzzled on the why's. My 94 4Runner 3.Slowww had the A/T temp light come on 1 week after I bought it, so I took it back to the stealership and they did a flush and refill. That was 4 1/2 years ago, no problems until now 62000 miles later. Just after purchase I had an auxillary cooler installed (do a lot of towing, boat, snowmobile, quads, ect.). Trans level is good, fluid color good, no burnt smell, no slipage or abnormal shifting. The light came on this AM for about 2 miles and went back off. Driving for about an hour at 70 mph, fairly smooth flat grade, -23F wind chill. Time for a new flush/tranny check/sensor/gremlins???

 

If you did a search you probably saw a couple of my threads on this subject. As there was no rhyme or reason for my light coming on, I installed a trans temp gauge so I could monitor it. Since I installed the gauge, the light hasn't come on. Some weird variation on Murphy's Law? But if you do a lot of towing, a gauge might be a good investment.