ok so my brother has a new topkick with an lly but it seems to have a dpf also how do i eliminate the codes it will throw when we eliminate his stock exhaust set up
Umm, if it's a LLY I believe that you're looking at the catalytic converter and not a DPF.
I believe LMM engine codes are the only ones running DPF's - McRats new highway Yacht has the LMM and DPF, I don't think yours does.
After reading your reply it sounds like I'm wrong and it does have the DPF - are you SURE it's the LLY motor?
Because looking here at the engine's it says 2006/2007 emissions (lly and LBZ motors like you said - but w/out the DPF being offered...) http://www.gmc.com/topkick/c4500/specsEngine.jsp