What is the difference between OBD-I and OBD-II?
Quick Answer
Earlier systems were manufacturer-specific; OBD-II standardized key emissions-diagnostic interfaces, with vehicle-specific functions remaining.
Earlier on-board diagnostic systems used manufacturer-specific connectors, communication and code conventions. Their adoption dates differ by market and manufacturer. OBD-II standardized important emissions-diagnostic interfaces, but manufacturer-enhanced functions and coverage still depend on the vehicle and scan tool. Do not infer compatibility solely from a model year or connector shape.