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Old 09-27-2020, 12:59 PM   #1
Junior Member
Join Date: Sep 2017
Posts: 24
Black Tank sensors/monitor

Ok, here are the particulars:
2018 Forester 3011DS, Have the small mounted tablet that shows all the switches and levels.

I was getting ready for a trip and flushing some excess water from my black tank. Looking at the monitor, it showed empty, nothing showing on the monitor. Also checked the phone app and this showed the same. I added some water thru the black flush (Black tank valve closed). I ran it for quite some time, checked by looking down the toilet hole and could see water building, but still nothing on monitors.
Emptied tank and decided to look at sensors. Pulled back the panel in the wet bay and revealed all the sensors for black and grey (grey is working just fine). If I ground the sensor wire, I will see this on the monitor. 1/3 shows 1/3, 2/3 shows 2/3, and full is showing full. I did this by using a jumper wire. I also re-crimped the single wire connection. There is a small block that all sensor wires run into and that looks all good. At this point I am not sure what my next step is to continue searching. Any thoughts would help.

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Old 10-05-2020, 11:33 AM   #2
Junior Member
Join Date: Sep 2017
Posts: 24

So, just a little update.
After working thru some troubleshooting thoughts, this is what I did.

Remove wet bay panel to access Black and Grey Tanks.
Ground out each sensor and watch monitor of response (Everything was showing good, all sensors showed correct levels)
Trace wires back to control panel behind drawers in wardrobe in bedroom. re-crimp all factory connections.
swapped sensor leads at control panel and systems followed wire.
Back out in wet bay, removed 1/3,2/3,and full sensors, cleaned and put back in. levels were responding a little better, but still not as they should.
Ordered new Horst Miracle probes, installed and tested.
Levels are now displaying correctly, ran 2 tanks of clean water thru black flush while monitoring from inside down the hole.

Would have not guessed i would have needed new sensors this quickly, but I guess they could have been sitting around in a bin for quite some time before being installed. The old sensors looked to be the Horst Miracle probes as well with the little teflon hood over the probes.
One thing to note as well, we have not run any solids down into the black tank, only liquids. (Been fortunate to be near very clean facilities, and hey why dirty yours when you can dirty someone else's. )
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Old 10-05-2020, 12:05 PM   #3
Head Rambler
Join Date: Mar 2008
Location: Southwest Alabama
Posts: 8,402
It's possible that you had some corrosion on the ring terminal at the sensor bolt or there was some buildup on the probe inside the tank. Likely the bottom most sensor.

Most sensor networks run at such a low voltage that even a little corrosion or buildup will affect the readings.

At any rate, I'm glad you got it figured out and fixed.
And I'm especially thankful that you came back and posted the fix, even after you didn't get any response to your initial question.
Salem 29RKSS Pushing a GMC Sierra 2500HD!
Gotta go campin!
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Old 10-05-2020, 12:30 PM   #4
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Join Date: Sep 2017
Posts: 24
I was hoping for some responses to help direct in a positive way. I know sometimes people read for information, so figured I would update so if anyone else had similar issues it would help them along.
The funny thing is the bottom sensor is tucked way back in on the left side and has limited access, so that is the only one I did not remove, clean and re-install. When I got the new probes, I figured I would just change them all, that way I am at a good known starting point.
The rings on the wires all looked good as well, if the probe replacement hadn't worked, then I was going after the resistor pack next.
Here is to hoping the new probes last longer.

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black, black tank, tank

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