ACT_

I had this issue...I had to release a bit of anger though, but for some reason, after throwing some nades and firing a missile at the stupid vehicle, It worked...and I got to the next marker. I would save just as your about to enter the vehicle, Then just continue with trial and error... Thats what I did, and eventually after some miserable attempts it finally worked... If it turns and starts driving around a house on route, then chances are that it's working...Just stay calm and keep trying.