Is purchasing a used 4 door passenger vehicle a part of operating start-up cost under section 179 ?

Yes, if the business purchased a vehicle in order to have it for business use as soon as the business started then it would qualify as a start up cost.

@jctcooter 

Could you clarify your question?

A "Startup Cost" is for expenses incurred before the business starts, but would have otherwise been deductible if the business had already been operating.

Section 179 and various depreciation options are for "assets" for the business, which are separate and different than "Startup Costs".