'99 S420 low coolant warning light is on. Coolant is full. Low windshield washer fluid warning light is on also. Fluid is full. Nearest dealer is 60 miles from here and car is not due for service for a few months. Does anyone know what might cause this other than 2 bad sensors and is it something I should have looked at right away? A few years ago the left side of the dash was loose and the dealer repaired it. That's about the only trouble I've had with the car. Thank you very much..... Terry

 

hello Im not sure about the washer fliud light but usually the sensor inside the engine coolant reservoir goes bad and gets corroded. the sensor is on a pivot, moves up and down with the coolant level probably sticking. hope this can help.

 

Thank you for your reply chassis 221. With the sensor unplugged it reads 109.5 ohms resistance and with the switch on the brown/black wire has 4.8 volts on it and the brown wire (the ground I guess) shows .3 volts. I wonder if these 2 sensors work on the same circuit and I have a grounded wire somewhere? Any suggestions will be appreciated. Thank you...Terry

 

Found this on another website:
"Well after talking with my friend at the mercedes dealer (he isnt that experienced with mercedes since he hasnt worked there very long and he did however tell me that the coolant level sensor is in series with the washer fluid level sensor. and if either is faulty it can trigger the other one. he also gave me some specs from netstar for the resistance on both switches. both have a resistance of less then 5 ohms with a low fluid reading and 110 for a full reading for the coolant sensor and 160 for the washer level sensor. " With that info I decided to drain the windshield washer fluid and the coolant light went out. So it looks like the problem is the washer level sensor. Refilled the washer fluid and the coolant light is back on. Drained it again and it went out. The windshield washer warning light stayed on through all this and is still on. Is the washer level sensor in the top of the reservoir or is it integrated into one of the pumps on the side?
Thank you......Terry