Is there any instance when a collection agency can repossess vehicles?

Is there any instance when a collection agency can repossess vehicles?
What is the collection agency trying to collect from. A car payment? If so, yes!

If its another debt like a credit card, you would have to be sued by them and a judgment entered against you first. Then the answer would be yes...

Generally, an unsecured debt is limited as to the assets they can seize. It varies from place to place according to local laws. Its possible, but unlikely.

On a car loan yes but not for an unsecured debt such as credit cards, no.