Bought CTS-V, Fuel CEL popped in the dealer lot

First post (of hopefully many) and unfortunately I need some help! Just pulled the trigger on an 11' A6 CTS-V. During the test drive, the car definitely felt down on power from what I would expect. For reference I've owned a C7 Z06, 17' LT1 SS, cammed f-body etc so I have a decent enough understanding of what roughly 500 whp should feel like and this was definitely not it. Looking around for any weird indications, I notice the boost gauge was at 0 under heavy throttle loads and wasn't moving at all as if the gauge was dead. Nothing I could do to the throttle would cause it to move and I assumed either the gauge was malfunctioning or the car just wasn't producing any PSI off the blower. After driving it for about 10 min, the boost gauge started working which triggered the belief cycle of "my butt dyno must be miscalibrated, it must be me" and that everything was fine. The car is pretty much impeccable everywhere else.

Well, it was not fine and I should've never second guessed the most reliable of performance instruments (Mark IV butt dyno). Literally upon going to pull out of the dealer lot, the car popped a CEL. Had the service guy scan it and he came back and said something something fuel relay. I asked for the code number and mysteriously no one knew what it was and no one wrote it down, they just cleared it out. Thought that was extremely shady because how do you as a professional service department scan a code on a car you sold 5 seconds ago and not know the code number. But I digress. Left the car at the dealer (90 day warranty and I technically haven't dropped off the check to them yet since it's the weekend and bank was closed) and they assured me they'd get to the bottom of it. While I don't doubt their intentions, if this is a fuel sending problem that's going to cost big bucks I can 100% see them being like "oh yeah we changed a spark plug and it's all good now" or some BS.

Not trying to put the cart before the horse and I want to give them the benefit of the doubt but I've bought enough cars to be able to envision how this is probably going to play out (i.e. it's in their best interest to try and say they fixed something trivial at basically 0 cost to them versus fixing the actual problem which is likely pretty expensive) and I'm just trying to be prepared. Outside of the obvious fuel pump and/or injectors, what are the common fuel issues with these cars? From what I could tell, the car looked bone stock & I don't believe it had a pulley on it. Obviously not to say the previous owner didn't have one on there and swap it back prior to the trade in.


Thanks in advance. Have wanted one of these cars forever and unfortunately stumbled upon one with some problems