I drive my own personal vehicle for my job and at least 80% of my driving is done at work.I get reimbursed for like 20 dollars a month for my gas.But what if your car needs to go to the shop.Is the burdan of paying to fix the vehicle fall on you or should the company pay to fix it?or because i don't write down the mileage am i stuck with it.I always thought they needed to have a vehicle for you to drive on their time.that they insure put gas in and to do your job.Am i wrong?

Yes, you are wrong. There is no requirement that they provide you with any vehicle allowance. It would be nice of them to do so and many companies will, but it is not mandatory.

Patty can tell you about the tax implications.

You may be eligible for some tax breaks for unreimbursed business expenses or other tax deductions based on the percentage of usage for business vs. personal. I recommend you see a tax preparer about the details.