A Cadillac I was driving had a warning light on the dash that said check water level. The water reservoir was full. We ran a computer scan and found out that the sensor in the bottom of the water reservoir was bad. The problem is that you cannot buy the sensor as a separate part, it comes with the reservoir. I have purchased similar sensors for $10-$20, the cost of the reservoir was almost $100.
It seems the manufacturers take a relatively inexpensive part that will fail often and combine it with a part that is expensive but rarely fails. This way they can sell more of the expensive parts.
