There has to be human mistake. Since your Chevy Blazer is not a 1996 or
newer vehicle, the Check Engine light portion of the smog check is conducted
by the smog technicians (as opposed to the smog machine via an OBD II
connection). Basically, if the smog technician observed a problem with your
Blazer's check engine light system, he/she entered into the smog machine and
your vehicle failed the test. You might want to re-visit the smog station
and ask the technicians to look at your Chevy again, if you insist that your truck's check engine light was not on.
posted by SmogTips Support