Joe Jonas -- I'm Certifiable ... In an Uber

Joe Jonas has found a new gig after the dismantling of his band ... he drives a fancy cab.

Joe has been officially certified by Uber to drive drunk and sober people alike through the streets of L.A.

The middle Jonas took random passengers to Pinkberry this week. The question is ... why?

We're told he's working with a mystery company -- not Uber -- to film a spot they hope will go viral. We're getting conflicting info on the company ... some people are saying MINI Cooper, but we're not sure.