Can a co-signer take the vehicle away from the primary buyer even if they have not missed a payment?

Of course not. The car belongs to the person listed on the title and to the lender who holds lien rights, and not to you. You own nothing here. The only interest you have in this vehicle is that you have guaranteed to pay the loan if the primary owner does not. They are making payments, so what is your problem? You have no rights to the vehicle at all. If you were to take the vehicle without the consent of the owner, you can be charged with theft of a vehicle. As long as the payments are being made on time you have no need to do anything.