Both companies are responsible, and both companies take full responsibility. Tesla doesn't make you go to the supplier. Also it's a very rare problem, so it's

Both companies are responsible, and both companies take full responsibility. Tesla doesn't make you go to the supplier. Also it's a very rare problem, so it's probably hard to find in QA. People (maybe not you) are still interested in the source of the problem, but it's an ortoghonal question.