If it turned out the door locks on the car were defective you'd expect them to be replaced under warranty. If the warranty had expired the situation would, admittedly, be a bit murkier - but you could still make a case that since the locks had always been faulty they'd be the manufacturer's responsibility.
Someone I used to work with had a car a few years ago on which the battery would mysteriously drain for no obvious reason. It turned out to be a defect in the infotainment system's firmware - and he was furious that he was expected to pay for the firmware update to fix it. (The car was long out of warranty, though.)