There are a number of OBD-II trouble codes that refer to either Bank 1 or Bank 2. There are conflicting messages on Bank 1 versus Bank 2, so we’re trying to set the record straight. Quite simply, Bank 1 refers to the side of the engine that has the #1 cylinder. Bank 2 is the opposite side of the engine. It’s not correct to simply state that driver’s side is always cylinder #1 or vice versa. Even on cars with a tranverse mounted engine, bank #1 is referring to downstream from the side of the engine with cylinder #1.