In Illinois, an auto repairer has a right to a "retaining lien". That means that they can hold the car until they're paid for their work. They lost that lien when they released the car to you. However, just stopping payment on the check might bring a lawsuit claiming fraud against you. If you can really prove that the work was as bad as you describe, you should probably protect yourself by filing a lawsuit against them in the Rolling Meadows courthouse. The small claims process should help bring this to a head quickly. I doubt hiring a lawyer will prove cost-effective because most attorneys in the northwest suburbs won't touch a case without being paid a fee of at least $500 and this isn't a case anyone would take on a contingency fee basis. Good luck!