Since it's winter and if you live in a cold area of the country that could be the reason it's not functioning. Here's some info I found on the effect of cold on the ASS system:
The conditions that will cause an automatic start-stop to stop working varies from model to model, but there is a common cause — think a climate control fan set to the highest speed, or the windshield wipers are activated at the same time as seat heaters and window defrosters. Not all models will indicate the system is offline due to any of these conditions via a dash icon.
Winter driving brings its own challenges to start-stop systems, and knowing if it’s a normal vs. abnormal offline situation may save you an unnecessary trip to the shop. Almost all of these systems systems use a smaller secondary battery — like the size used on motorcycles and ATVs. Like any other battery, these will have reduced capabilities when temperatures drop. If they don’t register a full charge, the system won’t operate.
They do recharge automatically through the engine’s regular alternator system, though. So if the engine hasn’t reached full operating temperatures (like on a frosty winter morning, for instance), the feature will be offline temporarily. On some models, if a temperature setting has been set on an automatic control system, the automatic start-stop feature will remain disabled until that temperature is reached.
Usually, if a start-stop system has a real problem, such as a battery that won’t recharge on its own or a sensor glitch, a warning icon will light up, messaging the driver that it’s time to get things checked out.