40 CFR § 85.2207 - Onboard diagnostic test standards.

(a) A vehicle shall fail the OBD test if it is a 1996 or newer vehicle and the vehicle connector is missing, has been tampered with, or is otherwise inoperable.

(b) A vehicle shall fail the OBD test if the malfunction indicator light (MIL) is commanded to be illuminated and it is not visually illuminated according to visual inspection.

(c) A vehicle shall fail the OBD test if the MIL is commanded to be illuminated for one or more diagnostic trouble codes (DTCs), as described in 40 CFR 86.1806.