SAI question

[Tailwind]

I'm getting ready to tear into troubleshooting my P0410/P1411 codes and had some questions for the experts.
When you activate the pump via Durametric, does it also activate the changeover valve?
If you do the above with the engine stopped, can you feel air coming out of the tailpipe?
My experience with this CEL is it did not trigger after the first 90 second run, and I did sit at a light for a couple minutes; then the next time I was stopped and the SAI ran for a second time, I got the CEL. I read the SAI runs a second time to "test the integrity of the system". What is this and why didn't I get a CEL the first time I was sitting after the first SAI? This happens every time I take the car out.

tia