The used vehicle credit is not specifically disallowed for married filing separately.
https://www.irs.gov/credits-deductions/used-clean-vehicle-credit
However, you should very carefully estimate your taxes both ways before you file. There are other significant deductions and credits that are reduced or disallowed under the married filing separately status, and you need to do the math to make sure those costs don't offset the benefits. Also, remember the most significant issue with MFS--if one spouse itemizes their deductions, both spouses must itemize, even if there are not enough itemized deductions to go around. It is not allowed to load all the itemized deductions onto one spouse so the other takes the standard.
