Two problems related to front seat heater/cooler have been reported for the 2005 GMC Sierra. The most recently reported issues are listed below.
Driver seat heater turns on by itself creating an extremely unsafe driving condition in the summertime in high density traffic with sun glare a problem and an inability to effectively turn the seat heater off. This problem has been reviewed both by the local Chevrolet and GMC dealers with the ultimate corrective action being to disconnect the seat heating elements. While this addresses safety for me it falls short of providing me with a functioning seat heater as purchased. Also the corrective action does not give consideration to a potentially general existing problem---which is the more important reason that I make this report.
The driver seat heater randomly turns on by itself. It randomly switches from the seat to the back of the seat to both at the same time, in no particular order. When I turn it off it just comes right back on again. I had the module in the door replaced one time, but it still does it. I live in the south, so it's extremely unbearable during the summer months. I will go for weeks at a time when it doesn't do it, but then it just seems to start again. There really does not seem to be anything in particular that triggers it. I thought maybe it was getting wet when it rains, but since I live in the south we have high humidity 95% of the time, so we have moisture problems here all the time. I can go for weeks that it doesn't happen, then it just starts up again. I have searched the problem on google and found that other people complain about the same problem with this particular model, but I can not find a safety recall issued by GMC.