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Discussion Starter · #1 ·
Hey everybody,

Just wanted to pass along some knowledge that I recently learned, though it may not be news to any of you. The DEF tank sensor apparently uses some sort of sonar to determine how full the tank is. Unfortunately, if you fill the tank right up to the top, it can't read the level at all: it needs some air to read properly (my only assumption is that it's measuring the speed of the sonar return through the two mediums of the water and DEF, since they would be relatively constant through differing environmental conditions, yet different from each other.).

I filled my tank all the way up, after the low DEF alert popped up in the cluster, and because it was too full, the gauge didn't move and the mileage countdown continued. After about 3 days, I topped it off again. Long story short, the counter went all the way down to zero and the truck wouldn't start. Luckily, I drove it to the dealership before I turned it off. The whole thing had the dealership scratching their heads too, but eventually they found some info about the sensor and were able to reset it and tell me how to avoid having it happen again. Hopefully this is helpful to somebody out there, and y'all don't make fun of me too much, haha!
 

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2015 Outdoorsman EcoD CC w/6.4' 4X4
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Interesting about the level sensor. I could see how if there isn't an air gap that it wouldn't work correctly.
I've worked with industrial liquid level sensors, both radar and ultrasonic based. The radar based ones are pretty wild as you can tune it "see" the water vs if there is foaming on top.
 

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The DEF gauge sensor does not go all the way to the top of the DEF tank that is why the DEF gauge will read full for so long, there is a video or two that show the DEF gauge from the Ecodiesel (and other Ram Diesel trucks) DEF tanks and explains how it works, it is a long thin strip sonar board that sticks straight up, when the DEF covers the sensor the gauge reads full, but because the gauge does not go to the top of the tank it will read full for a long time before the DEF gets low enough to start exposing the sensor to air. Once the sensor is exposed to air in the tank it starts showing the level drop on the gauge.

Once the DEF fluid goes above the stand up sensor it does not know if you filled the tank to the top or just above the top of the sensor because it will read full either way.

Here is a video that explains how it works:


It sounds more like you had an issue with your DEF gauge because once the DEF level went above the top of the sonar sensor it should have read full and again it does not know if you filled the tank to the top or just above the sensor it will read full either way and will not start to read the actual DEF level until the sonar board is exposed to air in the DEF tank and that can take a couple of thousand miles depending on how many gallons your DEF tank holds.

My 2019 Ram 1500 Classic Ecodiesel has an 8.4 gallon DEF tank, I think the newer Ram 1500 with the GEN 3 Ecodiesel only have a 5 gallon DEF tank. When I bought my Ecodiesel I put in 7 1/2 gallons of DEF on top of what was in the tank from the dealer, they did not fill up the DEF tank when I bought the truck.
 

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Discussion Starter · #4 ·
The DEF gauge sensor does not go all the way to the top of the DEF tank that is why the DEF gauge will read full for so long, there is a video or two that show the DEF gauge from the Ecodiesel (and other Ram Diesel trucks) DEF tanks and explains how it works, it is a long thin strip sonar board that sticks straight up, when the DEF covers the sensor the gauge reads full, but because the gauge does not go to the top of the tank it will read full for a long time before the DEF gets low enough to start exposing the sensor to air. Once the sensor is exposed to air in the tank it starts showing the level drop on the gauge.

Once the DEF fluid goes above the stand up sensor it does not know if you filled the tank to the top or just above the top of the sensor because it will read full either way.


It sounds more like you had an issue with your DEF gauge because once the DEF level went above the top of the sonar sensor it should have read full and again it does not know if you filled the tank to the top or just above the sensor it will read full either way and will not start to read the actual DEF level until the sonar board is exposed to air in the DEF tank and that can take a couple of thousand miles depending on how many gallons your DEF tank holds.

Not sure what to tell you: it didn't go back to full, and they didn't replace anything on the truck. I'm just passing on what the dealership told me, I'm in no way an expert on the subject.
 

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I just went through the manual for my 2019 Ram 1500 Classic ecodiesel, there is nothing in the manual about the DEF gauge not working if the tank is overfilled, the manual does warn not to overfill the DEF tank in temperatures that could freeze as that can damage the DEF system. When DEF freezes it will expand so if you overfill the DEF tank in freezing conditions the expansion of the DEF in the system can damage it from the expansion.

I said I thought the DEF tank was 8.4 gallons on my truck it is actually 8 gallons even.

It sounds like your dealer did a reset of your dash cluster and that fixed your problem and gauge started reading again. If the DEF system is frozen that can cause the DEF gauge not to read until the DEF thaws via the DEF heater.

This is right out of the Ram manual from my truck:

Filling the DEF tank in cold climates

Since DEF will begin to freeze at 12 degree F your vehicle is equipped with an automatic DEF heating system. This allows the DEF injection system to operate properly at temperatures below 12 degrees F if your vehicle is not in operation for an extended period of time with the temperature below 12 degrees F the DEF in the tank may freeze. If the tank is overfilled and freezes, it could be damaged. Therefore, do not overfill the DEF tank.

Extra care should be taken when filling with portable containers to avoid overfilling. Note the level of the DEF gauge in your instrument cluster. You many safely add a maximum of 2 gallons of DEF from portable containers when your DEF gauge is reading 1/2 full.

DEF fill procedure

1. Remove cap from DEF tank (located on the drivers side of the vehicle or in the fuel door).

2. Insert DEF fill adapter/nozzle into DEF tank filler neck.

NOTE:

*The DEF gauge may take up to five seconds to update after adding a gallon or more of Diesel Exhaust Fluid (DEF) to the DEF tank. If you have a fault related to the DEF system, the gauge may not update to the new level. See your authorized dealer for service.

*The DEF gauge may also not immediately update after a refill if the temperature of the DEF fluid is below 12 degrees F. The DEF line heater will possibly warm up the DEF Fluid and allow the gauge to update after a period of run time. Under very cold condition, it is possible that the gauge may not reflect the new fill level for several drives.

Caution!

*To avoid DEF spillage, and possible damage to the DEF tank from overfilling, do not "top off" the DEF tank after filling.

*DO NOT OVERFILL. DEF will freeze below 12 degrees F. The DEF system is designed to work in temperatures below the DEF freezing point, however, if the tank is overfilled and freezes, the system could be damaged.

*When DEF is spilled, clean the area immediately with water and use an absorbent material to soak up the spills on the ground.

*Do not attempt to start your engine if DEF is accidentally added to the diesel fuel tank as it can result in severe damage to your engine, including but not limited to failure of the fuel pump and injectors.

Caution!

*Never add anything other than DEF to the tank - especially any form of hydrocarbon such as diesel fuel, fuel system additives, gasoline, or any other petroleum-based product. Even a very small amount of these, less than 100 parts per million or less than 1 oz. per 78 gallons will contaminate the entire DEF system and will require replacement. If owners use a container, funnel or nozzle when refilling the tank, it should either be new or one that has only been used for adding DEF. Mopar provides an attachable nozzle with its DEF for this purpose.

3. Stop filling the DEF tank immediately when one of the following happen: DEF stops flowing from the fill bottle into the DEF tank, DEF splashes out of the filler neck, or a DEF pump nozzle automatically shutoff.

4. Reinstall cap onto the DEF tank.

As the video explains in the other post the DEF tank sensor shows full once the sensor stick is covered by DEF and is no longer exposed to air, trucks with large DEF tanks such as mine may take 2,000 miles before the DEF gauge will start to move off of the full mark and that occurs when the sensor is exposed to air. A truck with a 5 gallon DEF tank may only take 500 miles for the DEF gauge to start to fall from full on the gauge.

I think your dealer is mistaking overfilling in cold temperatures can cause the gauge to malfunction. Since we are in summer it is more likely you had another issue with the DEF system and the dealer doing a reset of the cluster cleared whatever the issue was and your gauge started working again.
 

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I just went through the manual for my 2019 Ram 1500 Classic ecodiesel, there is nothing in the manual about the DEF gauge not working if the tank is overfilled
Is it possible that your 2nd gen EcoDiesel DEF tank uses different technology than the 3rd gen EcoDiesel DEF tank? The OP posted in the 3rd gen section of the forum, so I'm guessing he has a 3rd gen EcoDiesel.
 
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Discussion Starter · #7 ·
Is it possible that your 2nd gen EcoDiesel DEF tank uses different technology than the 3rd gen EcoDiesel DEF tank? The OP posted in the 3rd gen section of the forum, so I'm guessing he has a 3rd gen EcoDiesel.
That could be. I have a 2020 Limited, not the Classic, so it could be significantly different than his 2019. He seems really angry about it though....

Either way, I'm going to trust the dealer over some random guy getting mad about my story.
 

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First time ever posting on a forum. I have a 2015 Ram 1500 Laramie Ecodiesel, and had the same problem as first discussed. I filled the DEF tank to the top and it started spilling out (my fault for not putting the right amount in) then only 5-6 miles down the road my gauge went straight down to the red. Only a 100 miles later I got the CEL and the count down started. I took it to the dealership and they went all crazy. Didn’t even look at my tank and proceeded to tell me I need a new engine. I just towed a 7K trailer with my family up to New Hampshire. Just trying to get more money. Since they didn’t touch the tank, which is why I brought it there I decided to do something I saw on another forum. If it works I’ll post it here. The first guy who posted to this isn’t crazy. That’s exactly what happened to me only my dealership didn’t help me.
 

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Based on all my reading so far, I think it's time we start naming names. There ought to be a thread where bad dealerships get called out so people can avoid them, and good dealerships that people can be steered to.

Much of our trouble comes from bad diagnoses, lazy/incompetent techs, shady service managers or general managers that run the dealership and so on. As owners, we should be helping each other find the good dealers and call out to avoid the bad ones. And maybe it's not a bad idea to include RamCares when calling out the bad, since they might be able to sort out some things from a manufacturer representative level, who knows?

Just a thought.
 

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Based on all my reading so far, I think it's time we start naming names. There ought to be a thread where bad dealerships get called out so people can avoid them, and good dealerships that people can be steered to.

Much of our trouble comes from bad diagnoses, lazy/incompetent techs, shady service managers or general managers that run the dealership and so on. As owners, we should be helping each other find the good dealers and call out to avoid the bad ones. And maybe it's not a bad idea to include RamCares when calling out the bad, since they might be able to sort out some things from a manufacturer representative level, who knows?

Just a thought.
 

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Based on all my reading so far, I think it's time we start naming names. There ought to be a thread where bad dealerships get called out so people can avoid them, and good dealerships that people can be steered to.

Much of our trouble comes from bad diagnoses, lazy/incompetent techs, shady service managers or general managers that run the dealership and so on. As owners, we should be helping each other find the good dealers and call out to avoid the bad ones. And maybe it's not a bad idea to include RamCares when calling out the bad, since they might be able to sort out some things from a manufacturer representative level, who knows?

Just a thought.
OK I can give you a start for Nor Cal:
Sacramento CDJR :avoid, service is horrid, service manager makes lots of excuses, but the fish rots from the head waited two years for the EGR recall service and was still 6 months away on their list when I got fed up and I called: Lasher Elk Grove CDJR awesome experience got me in in one week no issues - just went back for some warranty work on the differential again prompt scheduling and service. Elk Grove is way out of the way for me (22 miles) compared to Sacramento CDJR (6 miles) but it worth the extra drive.
 

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That's a start! If we get enough of a list, we could ask for it to be made a sticky. I can start a new thread with an appropriate title, so we don't hijack this one.
 
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