Is zakat obligatory on the cash amount owned, given that there are remaining car installments exceeding its value?

The remaining car installments are considered a debt. The preponderant opinion is that whoever possesses assets intended for personal use that they do not need should use them to offset the debt and then pay zakat on their wealth. As for someone who needs these assets, they should deduct the debt from the zakat calculation. There is no difference between immediate and deferred debt. It is a condition that the one paying zakat has no money to repay their debt other than what zakat is due on. If they have other money exceeding their basic needs, they should use it to offset the debt in order to pay zakat on their wealth.