How To Fix RV Holding Tank Sensors Guide (Full When Empty)

One of the more frustrating problems is when your gauge says full and nothing comes out at the dump station. This is one of the more frustrating issues RVers experience. It is time wasted and you are left guessing when your holding tanks are empty or full. Never a fun situation to be in.

The first step would be to give your holding tanks a good cleaning. You never know when they will get hard water deposits or other deposits covering those sensors. A good cleaning fixes many problems and keeps the sensors working normally.

To learn more about this issue just continue to read our article. It has the information you want to know about so you can fix your sensors, That way you will always get accurate readings and end the guessing game.

How do RV Tank Sensors Work?


The sensors are electronic devices that are placed at different levels to monitor your holding tanks. Those levels usually are at the 1/4, 1/2, 3/4, and 4/4 or full marks.

Their electronic signals go out continuously and when the contents of your holding tanks reach those levels, a light is supposed to illuminate on your dashboard. Those lights correspond with each level of the sensors.

In other words, there is a light at 1/4 full and so on. The fresh water tank should work in reverse of the other two holding tanks as you are watching the level as it goes down not up like the other two tanks.

When the sensors get dirty or are blocked, then they cannot do their job and your dashboard monitor gives out inaccurate readings. It is important that you keep those sensors clean and in good working order.

That way you should always have accurate readings and know when you should go to the dump station. Or at least when it is time to refill your fresh water tank.

Where Are Sensors in RV Black Tank?

This will depend on the type of sensor your RV’s maker decided to use. Their decision is usually based on cost, not precision. That will be one reason why you get many false readings.

Here are the three main types of sensors your brand of RV can buy:

1. Through the wall probe sensors- these stainless steel sensors are put in holes drilled into your black water or other holding tank walls. They are held in place by rubber bushings.

This type sends an electric signal to the dashboard monitor when the liquid covers the sensor and completes the circuit. These are the most popular of the three types of sensors

2. Electrical resistance- these are mounted on the outside of the wall of the holding tanks. They work by detecting the changes in electrical properties inside the tank.

This location prevents them from being covered by the contents inside the tank.

3. Acoustic/Ultrasonic - this is not one used by RV makers and is found in more industrial areas and holding tanks. They are supposed to be very accurate and are often used when hazardous situations can arise.

How To Test Holding Tank Sensors

This may be a problem for some sensors. One owner had to remove his water pump to get to the 1/4 level sensor. That is a lot of work. He tested it by removing the wire and using a meter to test for continuity.

Other owners did a visual inspection and found that their sensor was held on by a strip of adhesive tape. It was peeling away so they just put the tape back into position and their warning lights went away.

The simplest way would be to empty your tanks, then add water up to each level and see if the lights turn on at your dashboard monitor. Start at 1/4 and if it lights up move on to your next level and so on.

As long as you know the amount of water you are putting in, this method should be the most accurate way to know if the sensors are working or not. If a light does not illuminate, then you know which sensor needs cleaning or repair work.

RV Holding Tank Sensors Not Working


The first step is to clean your holding tanks. You first need to empty them and use your normal dump procedures to do this step. Then put in some holding tank cleaners, and there are lots of good brands on sale right now. Follow the instructions so that everything inside the tank is cleaned.

Then flush out the tanks like normal. After that, do the water test to see if any of the indicator lights do not light up. If they don’t, you know that you have either an indicator light problem or a sensor that needs repairing or replacing.

Replacing should not be a hard task unless, like that one owner, they are well hidden behind other key parts like a water pump, etc. As always, you can DIY this repair yourself if you are not under warranty.

Or you can go to your dealer or approved mechanic to get the work done right. You may be able to save some money if you buy the correct parts yourself and let them install them. There is a large markup on parts when the dealer, etc., buy them.

The Grey Tank Reads Full When Empty

This is a very common problem. It happens to almost every owner at some point in time. This is not a hard problem to solve as the source is that your sensors are dirty and not broken.

To solve that specific problem, you can use dishwashing liquid or special holding tank cleansers. Just pour a cup inside the holding tank, fill the tank to about half full and take a drive where you go up and down hills and make lots of turns.

You want to slosh that soapy liquid around well. Then dump the tank and rinse it out. If the problem persists, then you might have a loose or broken wire that needs tightening or replacing. Check the connections to make sure nothing is wrong.

The third possibility will be that the sensor unit failed and needs to be replaced. These sensors are usually on sale everywhere RV parts and accessories are sold.

This is either a DIY repair or a dealer repair. The choice is yours to make.

RV Tank Sensors Always Show Empty

The source for this is often some sort of solid waste that blocks the sensors. For black water tanks, it can be toilet paper or it can be other solids that find their way over to the sensor’s location and stay there.

For the gray water tank, the solids could be grease, food particles, and so on. You have to be careful what you flush down the sinks and the toilet when you are finished with what you are doing.

Usually, a good cleaning will take care of this issue for you. You have the instructions for this task in the previous section. To avoid the gray water tank sensors from becoming clogged, you should put screens in the sinks or at least some sort of filter in the drain pipe.

That way little food particles including solid grease can be stopped before they become a problem. Then just empty those screens and filters in your trash cans to be dumped at a later time.

You can’t do this for the black water tank so cleaning is your best option for when this happens to that tank.

How do I Reset My RV Tank Sensors?


This procedure is not for the actual sensors as you cannot usually reset them. You can reset the dashboard monitor and one method to do this is as follows:

Hold the pump tank and battery till the reset message appears then touch the pump, then the battery. The monitor will then need to relearn the sensors as you touch each of the buttons to read your levels.” (source- ).

There are a few more instructions on that forum. Not every monitor will react or be reset in the same way. You may have to look in your owner’s manual to find the right instructions for your model’s monitoring system.

Of course, if you are having trouble with the indicator lights and the system, it could be that there is a connection problem. The wires may be loose, crossed, or come out. If the reset system did not work then look at the connections.

The last resort would be to look at the sensors and make sure they are in good working order.

How To Fix RV Holding Tank Sensors

The steps to follow would be to start with checking your dashboard monitor. Make sure no parts are malfunctioning and test the lights to make sure they are working.

The next step would be to check the wires. They need to be in top shape, not corroded, rusted, or compromised in any way. The connections need to be tight and correct with no loose strands popping out.

Tighten and correct any issues you find with the wires. You can also use a multimeter to test the continuity of the wires to make sure power is getting to the sensors and back to the indicator lights.

Finally, you need to test your sensors to make sure they are working. If not, then you should replace them. The sensors may be hard to repair and find spare parts. The sensors are not hard to replace. They are located on the outside of the tanks.

How do You Change a Holding Tank Sensor?

The first step would be to shut off all power to the sensors. You can do this by removing a fuse or throwing the breaker. That way you only cut the power to the sensors and not other parts of your RV or trailer.

The second step is to take your screwdriver and remove any screws holding the sensor in place. You can remove any attached wires at this point as well. Or you can wait until you pull the sensor out of the holding tank.

The third step will be to attach the wires to your new sensors and then screw those new replacements in using the old screws if you want. You can go with new screws as well. Don’t forget to turn the power back on.

It is not a tough task and generally, all you need to do is remove the screws and rubber gasket and the sensor should pull right out. But like all other parts, this process may be different on different RV and trailer models.

How To Remove RV Holding Tank Sensors


The removal process will be the same as the repair or replacement process. There should only be a couple of screws to remove and a rubber gasket. Then the sensor should pull straight out.

The internal sensors should be similar in how you remove them. The key is to turn the power off before you start working. If you want to test those sensors, then wait to turn the power off until you have finished testing.

When you are done, do not forget to turn the power back on and test the new sensors. There is no guarantee that a new product will always work just because it is new.

Once you have completed replacing the old sensors, test the new ones to make sure they are in good working order. Use the water system to make sure those new sensors are sending the right signal to your indicator lights.

Can Tank Sensors Be Cleaned?

Yes, they can and it would be inconvenient to remove them and hand clean each one. You have to be a perfectionist to do that option. The best and most common method of cleaning the sensors is as follows:

1. Dump your tanks completely. Use the regular process you always use to make sure the gunk is cleaned out.

2. Fill your tanks 1/2 full with fresh water and dump in about a cup or 2 of holding tank cleaners. If they are expensive, regular dishwashing soap will do.

3. Let the tanks sit for a day soaking. When that time is over, take your RV or trailer out for a drive. You want the soapy water to slosh around. This reaches all the holding tanks’ surfaces.

4. Dump the holding tanks at a dump station and then rinse them at the same spot.

5. Refill your freshwater holding tank but first close all the valves. Then head back to your camping spot and enjoy the rest of the day.

How do You Clean RV Tank Sensors?

The process is as we just described in the previous section. It would not be a great idea to remove each individual sensor and give them a good cleaning. Something can go wrong with that option and you may be on the hook to buy a new sensor or 2.

You clean the sensors at the same time you clean the 3 holding tanks. That is the easiest and most convenient method to use. The key is to use one of the best holding tank cleaners that are on sale at most RV and other locations.

You should be able to find those cleaners at RV parts stores, big box outlets, and so on. Most do the job well and are affordable but when in doubt, use dishwashing liquid. That works well also.

Best RV Holding Tank Sensor Cleaner


There are different types of cleaners you can buy. There are the liquid, the powder, and the tablet options and each should do a good job of removing gunk and bacteria, etc.

Some top brands are:

Unique Sensor Cleaner Liquid

Camco 41146 TST Probe Cleaner

Thetford RV Level Gauge Cleaner

Caravan RV Sensor and Tank Cleaner

Valterra V22011 Sensor Power Tank Gauge Cleaner

Walex CMDOBG Commando Black Holding Tank Cleaner Drop-Ins

These cleaners are specially formulated to work on your sensors and are different from black tank cleaners. The latter cleaners are designed to break down waste and other solids. While you may clean the sensors a little bit, those cleaners focus on their primary duty.

Black tank cleaners are also good at unclogging RV toilets. Something the holding tank sensor cleaners do not do or are not good at doing. Just clean your sensors regularly and that practice may stop some inaccurate readings from taking place.

Some Final Words

Fixing sensors is like fixing any part of your RV or trailer. The first step is to check to see if you are under warranty or not. If you are, then let the approved dealer handle the repair or replacement.

If not, then this is an easy DIY project that you can do in your spare time. But to avoid these times, do regular cleaning to try and keep those sensors working at optimum levels.

Leave a Comment: