First of all, the vehicle has to be titled in the company's name for it to be listed as an asset on your business return. If the business doesn't own it, you don't put it on the return.
If it is titled in the business name, it doesn't start depreciating until you place it in service, no matter if it is new or old. So for instance, if you purchased the vehicle in 2018, and this is a 2018 tax return you are filing, it would have ZERO prior depreciation... that would come next year.
Can I at least expense the fuel for it?
Business use of a personal vehicle is normally reimbursed with an accountable plan, which has to be setup in advance and cannot be done retroactively.