OBD I (Vehicle model years 1988–1995)
In OBD I systems, when a fault condition occurs, the CEL stays on until the condition is resolved. This inhibits the driver from ignoring the problem. If the driver continues to ignore the problem, the vehicle will fail the next state-mandated smog check, which prevents the vehicle from being registered or "legally" sold. Some private sellers or dealers may attempt to sell a vehicle that has a code setting condition that is polluting the environment—this is illegal. Learn more >>
OBD II (Vehicle model years 1996–present)
OBD II is essentially OBD I with a new set of monitoring systems built on top. The monitors are bundles of software with increased testing capacity that either cycle constantly or when the system in question is in operational mode. Learn more >>