Tank Sensor Wiring Diagram

[Clotus]

Fellow Winnebago'ers,

I have a 2017 Minnie Winnie 31K. We picked it up as a prior rental and have been loving it for 3 years. I like that Winnebago uses the outside tank sensors as they have been absolutely accurate since purchase (first RV to reach such a feat). Well, they were accurate until last trip out. I was shocked at how long our gray tank was reading empty.

Crawled underneath and just as I suspected, there was a severed sensor wire hanging down. Worst part, the length of wire indicates the break is at the top of the tank where I cannot access to simply butt-connect back together.

Can anyone explain to me how the system is actually wired up from the sensors to the display? Is there one main +/- wire for all three sensors to the display? The empty light was lit, but no matter how full, the display never indicated.

If not, can someone point me in the direction of a wiring diagram. I found one on Winnebago's website, but it simply shows where it is wired, but not the close-up of the three sensors, how they are wired, and where I can tap into the wiring further in the coach.

Seems like a very simple circuit, but I am hoping you all can save me a lot of time and curse words

Any help is appreciated!

[imnprsd]

As you noted, no one really expects the Gray and the Black Water tank sensors to work... in older coaches... or wants to spend the money ($500+) only to later find these new sensors failed too, and then they are back to square-one.

Consequently, ss long as the fresh water tank sensor works, most of us find that acceptable.

However, I like everything to work in my RV so fixing my gray and black water tank sensors is a project I'm going to work on this summer.

My holding tank system is no doubt different than yours, but the principles should be almost identical when it comes to reading a probe and monitoring VERY LOW current in the line.

There are multiple displays in service too, but I think the problem with the display reading inaccurately is connected to the probe sensing circuit and the muck in the gray and black water tank.

I.e., muck in the gray and black tank makes it harder for the current to pass thru it.

As water levels rise current flows though the water in the tank (or muck). This "completing the circuit" ...and adds another resistor value (ohms) to the resistor ladder... which drives down the current... since the voltage is constant 5Vdc. ...And I suspect this is why your display usually reads empty more often when in fact your gray or black tank is fuller than that.

What you do know is that the fresh water (clear water) does work good. Even mine after 17 years of service, my fresh water levels never fail to read accurately. So at least we can count on that.

Also, your wiring diagram may have a few diodes to consider in the circuit; and I'm still not sure how the remote panel in the outside water bay receives it's information, but I suspect it is just a mirror (or slave) to the master panel inside the coach.

Note: Some RVs only have 1 monitor panel. Most of the larger Class-A's have 2 holding tank monitor panels.

Good luck with your fix. Maybe we all will learn from you when you are done?

* The diagram below may or may not be correct. I'm still verifying it.

In closing, to my knowledge there is not a thread that has nailed down a definitive fix to this problem. Maybe this one will be it? ...And maybe sharper/smarter tools in the shed will find this post and let us both know where to begin or to give up the good fight?

[Elkman]

Problems with the sensors on older RV's is that they were located inside the tank and with the black water tank the sensors would need to be hosed off periodically - I bought a special sprayer wand designed for this purpose. With out 2021 Navion the sensors are on the outside of the tanks which should help a great deal. But as I suspect with most people, we dump when there is a dump station along our route or at the campground as a matter of convenience, regardless of the level in the tanks.

[Morich]

Totally different operations on older senser and newer as the new do not have anything inside the tank, only higher tech pads on the outside which I "think" senses capacitance rather than closing a circuit.
This is info as explained to me by another forum user but seemed rational!

It would take some search to find the info but as I remember, the wiring is not a straight forward series or parallel but something different that the info we had did not explain how it worked, just that there are pads with electronics which send that info to boards at the monitor where it is then "decoded" to which light is lit.

Their solution, after talking to Winnebago and several others, was to replace a board at the monitor as there are at least two versions one old, one new and different colors like red board or green board.
As remembered, Winnebago was aware of the different boards but it is an outside supplier who provides the sensing wiring and pads.

This is the drawing info that I find but it doesn't give me much as it seems to be a set of daisy chain without much info on what and how it works:
https://www.winnebago.com/Files/File.../000200447.pdf

[Clotus]

Thanks for the replies. I have the newer sensors which mount to the outside, hence why they actually work. Thank you Morich for the drawing, it gives me a starting point. When I get a chance to get the MH home and get underneath it, I should be able to figure this out. I will report back if I determine anything helpful.


I'm hoping I can actually reach the other side of the severed cable and easily reconnect it, but highly doubtful

[imnprsd]

Like I said, no one has posted a definitive fix. You can try using different tank sensors, but I think it's going to come down to building a better mouse trap.

This sounds daunting, but wouldn't you think Winnebago would have come up with a solid holding tank monitoring system after 20+ years! I.e., they are either that stupid or that cheap, and I'm guessing it's the latter.

I wouldn't know, but maybe someone can tell us at what point Winnebago did start shipping 100% solid, working, never needing a repair, holding tank monitor system?

=== For us older RV owners looking for a definitive fix, I suggest you post your comments on this thread:

https://www.winnieowners.com/forums/...rs-360442.html

I hope to get to this project soon and I will post my findings when I can tear into my vintage holding tank system.

Summary

The probes vary, but the principles of the resistive ladder are the same in old and new designs. I think it is the display board that is different.

...And the basic problem is that these board are working with 25 milli-amps or less. Which is why the gray and black tank have problems vs. the fresh water probes that do NOT have problems. Even the 20 year old type of probe.

Here's a link that my prove to helpful to understand these tank monitoring systems.

https://instrumentationtools.com/bas...rrent-signals/

PS
Hosing down the black water tank almost never works to get your tank sensors working again, but hosing down the tank is good for sanitary purposes and to keep the smell down. Same goes for putting ice cubes in the black water tank.

[Elkman]

I would suspect the problem has more to do with the voltage used for the sensors than the amps they draw. With small gauge wires a voltage drop will affect a digital device much more than an analog one.

Winnebago is not in the business of manufacturing the items that go into their motorhomes and relies on its suppliers to do the innovation and provide reliable products at a cost that works within the product managers' budgets.

No idea why people are so hung up on TPMS which only became available in 2007 when the feds mandated them for passenger cars and light trucks as a way to improve overall fuel economy.

[imnprsd]

I think you are missing the point:

* The voltage is constant.

* You are varying the resistance in Ohms so you can measure the current in amps.

V=IR

What I am not sure about is if comparators are used in the old design and/or if DACs are used in the newer designs? I haven't investigated that part of the circuit so far, because I have not examined the part numbers on the back of my circuit board.

As for sensors, they all are just fixed resistors.

However, I would agree that if you you had higher voltages, with the same resistors, then your current will be higher.

I think my old style circuit board is 5V. Maybe your new circuit board is 9V?

That said, if you are working with more current and your black and grey holding tank status lights are still not working accurately, then what is the better mouse trap?