Anybody else seen a 2563 code on an LLY ? A friend installed 4" (downpipe back) Banks and after a few hours, got this code....cleared....again....cleared...and so on. Say's it seems to do it more @ idle? General told him that p-2563 was fueling mixture too rich:confused: . I thought these trucks were supposed to compensate for this through the computer:confused: . Any help would be apprec. Thanks, Ed.

this sounds like what happened on my truck. I installed a complete exhaust kit and started smelling fuel, etc.. my point is.. the diesel mechanic told me that the LLY when exhaust is installed the EGR does not get the right reading of backpressure and thus gets mixed readings on the MAF. The result is it not knowing how much fuel to send to the injectors and you get too much fuel and fuel in the ehaust..which is what I had.

not saying this is your problem too, but I do know the LLY is sensitive to exhaust mods from personal experience.

come to think of it...he did say he noticed a hint of smoke and thought he smelled fuel! (he never could pinpoint the light smoke?) So, anyway, how did you get the SES light to quit?

Found this in another post, may help you
http://www.thedieselpage.com/duramax/LLY04.gif