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