Your ABS sensors are the main tool that your ABS system uses when sending signals to the computer. If one of the sensors fail, a warning light will appear on your display alerting you of the situation.
When an ABS sensor fails, the system no longer operates. When a time comes when you are expecting the system to kick in, it will not, a dangerous situation if the driver is accustomed to it.
Replace your worn out or broken sensors and make sure that everything is up to the task of snow, ice, and wet roads.