Ok, I'll confirm that I said that. No problem.
Meanwhile, if you want to understand it for yourself, instead of taking my word on it and having me merely confirm it for you. Google "GM DTC P0401". Read various things. What you'll learn is why a map sensor might cause a flow code and why it's not necessarily a vacuum or EGR issue.
Sometimes codes are named poorly. In my eyes, this is one of them. it has EGR in the title and maybe GM found it to commonly be an EGR. I've seen it typically be anything but the EGR. Hence.. what monitors the flow in the intake manifold? Right.
