Aaron's rep tells TMZ ... Aaron was on the road promoting his new single when his car went out of alignment, so he decided to get it fixed at an AutoZone in Cornelia, Georgia.

The rep says Aaron wasn't even in the car when he was arrested, and there's surveillance footage to prove it.

As for the weed charge ... we're told Aaron has a medical marijuana license since he suffers from anxiety.

There's also this ... Aaron's blasting his older brother Nick for tweeting about the incident, saying, “If my own blood truly cared about my well-being, why wouldn’t he call me directly and have a conversation instead of making this about him through a very public forum? That’s not cool at all to use me for his PR and kick me while I am down. I love my family despite it through thick and thin.”