Check the fuses and relays in the underhood fuse box. Your car may have one or two Maxi-Fuses for fan power as well as 3 relays.
With any HVAC function set that calls for A/C compressor operation, fans should run in SLOW all the time. With no such HVAC setting, fans are controlled by the ECT and PCM - they go to SLOW at 224 degrees and FAST at 236.=QUOTE]
Beg to differ, but cooling fan operation is different for 06 on up. Fans do not come on when the a/c compressor is running, the pcm controls the fans via coolant temperature and refrigerant pressure. I know this for a fact based on my 06 and 10 DTS's. This is also stated (vaguely) in the factory service manual.
To the original poster, my 06 had a few cooling issues which directed me to look at the fan operation. One thing I did find which may relate to your problem is that the 06 and newer are very sensitive to even a slightly lower coolant level. I didn't prove this, but as mine ran past midscale on a few occasions after ascending or even waiting for a traffic light on a steep incline I suspect air may have worked it's way from the tank to the engine. The tank on these models does not provide much head for the system like the older Devilles do. You must check the coolant level cold. Do this before you do anything else.