Find someone with a good CAN scanner that can read more then just the general powertrain module. What would show up on an autozone reader(if anything) might just give you a general indication. Better then nothing, but it could still leave you wondering what it is.

From my one experience with the Wrench light, I would say that it's limp mode til it gets fixed. Could be wrong, but based on my experience, I was in limp mode when it came on for me.