Persistant Coolant Light!!
 

I have been having a problem with my Coolant Level light being illuminated for nearly a year now (SLK32 '03). I did run low on fluid at one point and after refilling, the dash warning did not go away. I thought I might have a bad sensor, so I replaced the coolant level sensor. That didn't fix it, so I tried filling up the washer fluid, and then replacing the washer level sensor. I considered that I might have the wrong fluid, so I bought mercedes fluid and did a coolant fluid drain and replace. None of these things have worked so far.

At this point I did a visual examination of the wires and fuses, which showed no obvious fault. I checked the plug for continuity, and it is indeed a closed circuit. The only thing I can think of is that the float is stuck in the down position. I can't seem to find a way to get at the float though. I loosened the tank and shook it around to no avail (a rubber mallet didnt help either).

When I unplug the coolant level sensor, the light remains illuminated and the washer level indicator does not illuminate.

Is there an easy way to un-stick the float, do I have to replace the coolant tank, or is there another common fault I can check for?

Thanks for the help! I'm excited to hopefully finally finish this fix.

Coolant reservoir & w/s washer sensors are connected in series.
Most likely a sensor going open or short circuit.

Well I replaced both sensors, and I checked the coolant harness for being a complete circuit. Is there anything you might recommend I could do to narrow it down?

Have you check the resistance values of both sensors?

maybe you can try sticking a bent coat hanger inside. fashion something straight and maybe you can reach in and "unstick" the float.

i did something similar with my washer fluid reservoir, filled it up but the light was still on so i reached in and got hte float to move up and work.

It ended up being the pre-fuse for the radiator fan. I took it in, had it scanned, and the light was being caused by "faulty ground or broken fuse". I was only aware of three locations for fuses, so I didn't find this one which was in a fourth location. Any which way, the light is out!