Let me give you a bit of advice of a common mistake people make when they start having vehicle problem and they contemplate or actually stop making payment on the note, DO NOT DO IT!. Even if your vehicle note is through GM financial, your note and warranty issues are two different worlds and stopping payment on your note thinking it will leverage a result for your vehicle warranty issues is misguided. All it will do is ruin your credit.
Until you either "Lemon Law" it or find some other civil solution with GM on your vehicle, you have to keep your loan current on payments.