A low coolant level sensor is an alert mechanism in most vehicles that alerts the driver when the engine coolant level is low. If the level of coolant in the engine falls too low, the engine could overheat and cause harm to the vehicle.
This electric sensor floats on a bobbing device located in the coolant tank and triggers a dashboard alert when the bob falls too far. In most vehicles, the sensor alert triggers an icon to light up on the dashboard. The icon is typically characterized by a key-like design floating in a wave, but can vary depending on the vehicle model and year.