Your original description can be a bit confusing.

Are you complaining about:

(1) player not powering off in-car?
(2) player not finding hard drive?
(3) something else?

If (1), then CHECK THE AC/DC POWER STATUS from the Hijack menu. If it incorrectly shows "AC/Home" when in-car, then that should explain why it fails to power off correctly. The solution in this case is to replace the "AC" power jack (which contains the contacts to distinguish AC/DC).