MOST later Land Rovers use a sensor probe in the coolant expansion tank to monitor the coolant level, giving a visual warning on the instrument display if the level becomes low. Like all electrical components, the sensor can fail, resulting in warning messages and warning lights being displayed even when there is adequate coolant in the system or, worse, showing a misleading correct level when the coolant is dangerously low. In the case of this 2010 Discovery 4 with 195,000 miles on the clock, it was the coolant level sensor probe that had failed and was giving a false reading, suggesting the coolant level was low when, in fact, it was at the correct level.
