I was riding with my friend on the way back from the range and a question popped into my head. He was driving and I was in the passenger seat with my gun in my holster. He doesn’t currently have a CPL but I do.
My question is, is it legal to carry as a passenger if the driver doesn’t have a CPL in Michigan?
@Brian542 Welcome to our community, We are glad to have you. 
I would say yes. Your CPL has nothing to do with your friend or his vehicle.
As long as he not a felon or you give it to him to stick in his pants. 
welcome from the Keweenaw of Mi.
you are your own entity as far as CC is concerned
but it would be wise to chose your friends carefully
Welcome to the family brother @Brian542 and we are glad you are here. I do not think there would be a problem with you as a passenger having a CPL.
Welcome
There again, a hodgepodge of laws complicated by the spider web of Federal, State, county and municipal laws all woven into one big mess.
Welcome to the Community @Brian542. I hope the answers you received thus far has been a comfort to your concern. Stay safe and remember, that is your firearm and what you do with it or what you allow to happen with or because of it is your sole responsibility when away from your own premises. Just be sure that you keep your proper ID with you and don’t fidget and provide unnecessary challenging conversation to the LEO while carrying, and if you have a duty to inform, do so when the officer approaches, and keep your hands in plain sight at all times, and don’t be helpful and try to show him that you have one or where it is. Only do as the officer asks or commands and only that, regardless of who you’re with. If he asks you to remove your weapon, DON’T. Ask him or her to remove it from you. Arrive home alive. Best to you, Brian542. I’m only hammering because I’m originally from Detroit. I know how things can get tense really fast. However, on a positive note, I’ve had a few encounters with LEO while carrying, and have had nothing short of a polite and peaceful outcome.