Something that's faulty is full of mistakes — it's wrong. Faulty logic often leads people to make terrible decisions, since they're based on an incorrect way of thinking.
A faulty explanation is based on errors, and a faulty machine doesn't work the way it's supposed to. If your chocolate chip cookies keep coming out burned, your stove may be faulty — or you may be baking them too long. If your car's brakes are faulty, it won't stop as quickly as it should, and if your furnace is faulty, it will be a long, cold winter. Faulty and fail share a common Latin root word.