The electronic brake control module monitors the ABS system during start up and during vehicle operation. This initial test is referred to as a "self test". During the self-test the amber light may remain on for 3 to 5 seconds. The light is turned off if the system passes the self-test. Should the module detect an error, it will illuminate the amber ABS warning light and disable the antilock function. While you are driving the vehicle, the module monitors wheel speed data from each wheel speed sensor, and controls the hydraulic assembly during an ABS stop.