I changed my oil and filter and now a code B16 showed up?

Sounds like mileage has elapsed allowing the maintenance minder to show a B service. I would recommend going with a mileage schedule if you aren't sure; every 5,000 miles for oil and filter changes, a tire rotation each time, and a multi-point inspection. The differential service should be performed roughly at 15,000 miiles first, and then every 30,000 additional to that. Hope this helps.