Thanks for the reply
The picture I stumbled upon to was in this thread
http://www.camaro5.com/forums/showth...hlight=exhaust Post four and five. Post 5 Picture was blurry. In the written Manual it was in section 9 - 890 Engine Exhaust. And It had something to do with "Exhaust Tail pipe flow valve mechanical system diagnosis'. And maybe there is more in that section about the functioning and the parameters of the dual mode exhausts too.
and I would have thought that it is the same system for zl1, ss, and lt if fitted (?)