It really depends on the lender. Generally, two or three consecutive payments can lead to potential repossession, beyond damaging your credit score tremendously. Some lenders will even consider repossession after one missed payment.
The good news is that you usually have options to handle a missed payment before things get out of hand. Be upfront with your lender about your circumstances and try to work out a solution.
Some ways to help lessen the burden of your car loan include: