While I don't know that I would consider myself a vocalist of any sort (and many around me would agree) but I found for me that there are kinds of vocals I can do in some adequate way. You may not be a good vocalist in the style or with the type of voice you desire but you may be good in another type/style.

Along with a vocal coach, when you're doing the 'car sing-a-long' try different style if you can. Most important, as you sing along with things, stick your finger in your ear. It's like having a little vocal monitor but will give you a clear indication of your voice. This also helps you hone in on vocal issues too.

Anyway, don't give and find where your voice is actually at.