My employer reported a car allowance of $2200 (unaccountable plan) on my W2 which did not cover all of my expenses. Was the car allowance reported as income in error?

Non-accountable expense reimbursements (where the employer does not require proof of expenses) are always taxable income.  While the employer could switch to an accountable plan if they wanted to, they are not required to.  This is something you may want to negotiate with them.