I recently had the engines malfunction light to illuminate; I took it to an autoparts store and had it diagnosed. The code said DTC 27 and DTC 28. When I looked inside of the repair manual it was described as Quad Driver module 1& 2 but I dont know what it's pointing to.
That's the high-current transistorized switching circuits that drive the ignition coils or injectors. Typically those are inside the Engine Computer but on some GM ignition coil packs they are built into that.