Black Tank Sensor shows Empty - even when full!

[DavidLyle]

I searched for a solution to my problem & found all kinds of posts about sensors being stuck on 1/3 or 2/3, but not always showing empty.

I have a 2008 Itasca Sunova 35J and recently noticed a problem with the black tank reading E at all times, even when I fill it up with water.

The gray and fresh water tank readings work fine as I see them fluctuate.

Any thoughts on what might be causing this? If the sensors in the black tank were dirty, wouldn't they be showing 1/3 or 2/3 full (as seems to be the common problem)?

Thanks,
David

[Chuck 1935]

It could be a bad ground connection that is causing your problem. Almost everyone seems to have problems with the black tank sensors. When I am on the road I put a jug of simple green or the equivilant and let it slosh around for a few hundred miles, then dump and rinse the tank, that may or may not fix it. Keep in mind, no matter what people say about you it takes alot to fill that black tank !!

[emmmw]

Similar problem here with the same coach. On ours the empty and 2/3rd lights are always lit whether empty or full. The Sunova/Sightseers' sensors are TrueLevel sensors and do not penetrate the tank so the responses you get about ice cubes and cleaning just don't apply here. We've also had no problems with our gray, fresh water and the propane tanks. I spoke with Winnebago when this first occurred and they said that it could be several issues including the way they gather and fasten the electric cords at the sensor or the closeness of things to the back of the sensor where it is stuck on the tank.

Good luck with this problem. I'm just resolved to put up with it and watch it through the toilet. I will be watching this one for a possible fix. I may change out the sensors in the Spring if I can purchase replacements...

[Dr4Film]

When it comes to the sensors, there are so many possible answers to the problem. However, I would agree with Chuck in checking to make sure the ground is really clean and making good contat. Another is that if you have a calibration port underneath the sensor bank, it could be maladjusted in that it would always read empty no matter what.

If you cannot locate the answer, you can always install an aftermarket unit just for the black tank. Not knowing how full your tanks are is a PITA.

I recently had to change out a light fixture in the kitchen as it was causing false readings on my level sensors. You just never know what can screw stuff up in these sophisticated RV's.

If the level sensors are partially lit such as emmmw's case, it would make sense to me that some of the sensors have crud on them which would need to be cleaned off. Using a good sensor cleaner and a power washer or wand to scrub the interior walls and sensors really good, I believe that may solve your problem.

Dr4Film ----- Richard.

[goforjoe]

I do this once a year, I go to Dollar General and by 40 dental tabs (the cheapest pack) for cleaning false teeth, I open all the tabs then fill the comode with hot water and put the tabs in over night and dump in the morning. My sensor lights work much better. Good luck.....Joe O.

[laplatarosa]

We have a 06 Sightseer 35N. Our black tank sensor always read like emmmw's. I've even disconnected the wires going to the sensor with no change in the display. Any ideas will be appreciated.

Thanks

[Clay L]

The three TrueLevel sensors on the side of each tank are active (integrated circuit) devices in series. As the liquid level rises and each sensor "closes" it causes a change in a voltage on the control board.
The control board uses LM339 Low Power Low Offset Voltage Quad Comparator ICs to sense the voltage change and activate the appropriate LED. There is no adjustment for this - at least not on the early boards. There is an adjustment for the propane which still uses the old style potentiometer sensor.

If either of the two wires from the sensor string are broken or has a bad connection none of the three LEDS for that tank will light.

If the tank walls get enough crud coated on them the sensors will be fooled and close even when the liquid level is low since the crud contains some water.

[Gary CA]

You will most likely continue to have this guessing game about tank levels. One of the best modification I did when the coach was new was to add this See-Level-II system. It takes time but I know exactly where all my tank levels are.
SeeLeveL Gauges by Garnet Instruments Ltd. - Model 709

[Greybeard]

We had the same problem w/ our 08 Vista. Our dealer replaced the contorol board or display panel inside the RV and it works fine now.