How can you determine if a vehicle's ABS is functioning when starting the engine?

To assess the functionality of a vehicle's Anti-lock Braking System (ABS) at the start of the engine, observing the behavior of the ABS light is crucial. When the engine starts, the ABS light should illuminate briefly, indicating that the system is performing a self-check. If the yellow light stays on after this initial illumination, it signifies that there is a fault or malfunction within the ABS. This is a key diagnostic step since a continuously illuminated ABS light means the system is not operational, which could compromise vehicle safety.

In contrast, if the light only comes on briefly and then turns off, it indicates that the ABS is functioning correctly. The other options—such as the light turning green or not illuminating at all—do not provide accurate indicators of the ABS system's status. Therefore, the prolonged illumination of the ABS light indicates a potential issue that requires attention for safe vehicle operation.