Much of this would likely depend upon where the firearm was in relation to you within the vehicle. While laws vary state to state and it is always advisable to consult with an attorney licensed in your state, generally speaking possession within a vehicle usually turns on who is driving the vehicle and where people are sitting. If you are driving the vehicle, the case against you is far stronger because you have control of the vehicle and are assumed to have knowledge of what is in the vehicle. If you are a passenger much of this would turn on whether or not you had knowledge of the firearm being in the vehicle and its proximity to you. Once again this is generally speaking and it is always advisable to consult an attorney licensed in your state to discuss the particulars of your case as every case is unique.