2005 Buick La Crosse code PO411

My back yard mechanic told me to get secondary air pump only could get one from dealer, they had to order one, so found a used one via internet it doesn't look like what he told me to get
questions: could you tell me how to correct po411, show me a picture of sec air pump & where located on engine have 3.8 series 3 when reset codre light stays out 2 days then comes back on
also my air bag light comes on every 6 months or so stays on from 2 minutes to sev hrs this goes on several weeks then ok another 6 or so months2