Oil leak

Maybe. It could get stuck on or it could not be coming on at all.

Well it is not that then. Something has got to either be plugged up or the valve on the pump is jammed.

There is a check valve in there. I *believe* it is in the hose leading from the pump to the exhaust. I am attaching a diagram that is provided by GM. Personally, I would bet that that check valve is not opening and that is what is causing your issue. It is likely a dealership only part, but it would not hurt to try the local auto parts shops and rock auto.

Something like that. I haven't specifically heard the one on those cars, but that's the general gist of it. Find that check valve. Replacing it shouldn't be expensive (Check valves aren't exactly new and exclusive technology).

Well from what I understand, the code indicates that there's some sort of flow error from the pump. So if you're hearing the pump run, and feeling it blowing air, then there has to be a blockage or something along those lines.

I suppose that it's possible that the oxygen sensors (readings used to set this code as well) could be reading incorrectly. But I doubt it. They'd have to not change as expected when the pump was running, which seems unlikely to me, especially without any other oxygen sensor codes.

There has to be an airflow issue somewhere in there. If the pump is pumping air, then there's something else going on. Either no air is getting through (jammed check valve, clogged tube) or too much air is getting through (check valve stuck open or a leak in the tube).