Both.

 

The St. Louis Gateway Vehicle Inspection Program (GVIP) is an OBD test. No visual test is made for emissions. If you are using an anti-fouler, running off of the stock computer, and not throwing any codes then you pass. If you are running a piggy-back unit and do not throw a code you can pass. If you are running a standalone, you fail. Also, do not try to clear a code by unplugging your battery right before the test, if your monitors do not contain enough data (displays as "Not Ready"), you fail.