Rear Ceiling Vents

[Suprrg]

2016 Suburban has no air flow coming from rear ceiling although I hear the blower motor perfectly in tune on each setting

 

[B-train]

My guess is the actualtor door to change from floor to ceiling has failed. It's not too bad of a fix once you pull off the passenger rear interior panel. But, a 2 way scan tool would help diagnose. You might be able to manually override it when you gain access. I had to replace one YEARS ago on my 2003 yukon.