If your glow plugs or intake air heater is not working on your Duramax engine, one of the problems could be a blown fuse. This fuse protects the main power circuit to the glow plugs/IAH.
Fuse is mounted under the plastic fuse panel cover in the underhood fuse block mounted on the drivers side fender
2500HD 3500 Silverado Sierra 6.6L V8 Duramax diesel:
2001, 2002, 2003, 2004 early