DEF Gauge Shows Empty When Full? Why This Happens (And Common Fixes)

What can you do when your DEF gauge shows empty when full? Is this something to be concerned about?

The DEF is a type of fluid made up of urea and a deionized water. It has a 1:2 ratio of these two components. Now, it has a reservoir that is different from your diesel tank. This fluid is then released into your exhaust streams in certain portions, which helps in regulating emissions.

Once the fluid is into your exhaust pipe, it will then vaporize and decompose. This will lead to the production of ammonia and carbon dioxide. These compounds create a reaction when mixed with nitrogen oxide and oxygen in your SCR catalyst. Thus, harmless gasses are produced such as water vapor, carbon dioxide and nitrogen.

But what happens when your DEF gauge shows empty when full? What should you do about it? Keep reading to learn more.

def gauge shows empty when full

Why The DEF Gauge Shows Empty When Full

The DEF gauge is responsible for notifying you when there is a low or zero DEF fluid in the reservoir. This gauge can be found below your fuel gauge. When your fuel is down to 10 percent, you should get the initial warning light. Then, once it reaches 5 percent, you will notice the light flashing. At 2.5 percent, the light will turn to a solid amber color.

But when it is at zero level, this will cause your vehicle to slow down significantly at 5 MPH. This is why you need to refill it to keep the engine running.

If you want to know more about the current DEF level, you can check it in the reservoir. It is right next to your diesel fuel tank, if you have a truck. Or in the case of cars, the tank is located close to your spare tire bay.

For newer vehicles produced in the year 2010 or so, there is a warning system on the dashboard that sends an alert when you have an empty or low DEF fluid. But if you see that the DEF gauge shows empty when full, this means there are issues involved.

It is important to note that as with other types of fluid your engine needs to operate properly, the DEF fluid is just as essential. This is why you should make sure you always have this fluid in the right level. It is required for cleaning toxic pollutants before being released into the environment.

Hence, you should make it a point to top up your DEF. Thus, if you see that you are running low on this fluid as shown in your warning system, you should quickly add more. Once the DEF completely runs out, you run the risk of experiencing downtime. You may even need to get your vehicle repaired and rack up thousands of dollars in bills.

Now, you may be wondering why your DEF gauge reads empty even if it is really full. There are many other people just like you who encounter this issue. This happens to those who have a diesel vehicle, which is why it is important to know why this happens.

One of the possible cause of this problem is when you have underfilled or overfilled your tank. This can cause your DEF gauge to have glitches and give incorrect readings. As a rule of thumb, you should leave about a third of your DEF reservoir empty.

Never fill your DEF reservoir beyond the top portion of your tank. To know how much you should put in the tank, simply unscrew your cap and check inside. You should be able to see the spot where the neck and the DEF reservoir are joined. 

This portion serves as the DEF’s breathing space. This is why you should never fill the tank over this portion. When you cap this neck off as a result of overfilling, this will cause the DEF within this part to crystallize. Hence, it prevents air from getting into the tank. As a result, the DEF is unable to flow from your tank to your exhaust streams.

When this happens, the system then senses an insufficient amount of the DEF and reads empty even when it is really full. Additionally, capping off your DEF tank’s neck leads to an underperformance of the engine. If you fail to fix it accordingly and prompt, the extra DEF will freeze and will clog up the reservoir.

It is also worth noting that you should never add DEF into the incorrect tank. This is why you need to first check the tank where you dispensed this fluid. If you end up putting it in the incorrect tank, simply avoid powering up your engine. 

You should also refrain from moving your vehicle from where the tank was filled. When you move it, this can cause the spread of the fluid into your SCR and engine lines. No matter what happens, never start your engine if you are aware the liquid was placed in the wrong tank.

Starting it up can cause serious damage that can be quite costly to repair. Do keep in mind that it is expensive to replace an SCR catalyst. So, the best thing to do is to simply drain the DEF right away and put it into the right tank. By doing so, you can fix this issue with the DEF gauge reading empty.

There is also the case of malfunctioning DEF sensors. When the tank indicates you are empty of DEF, this means that your sensor may be problematic. So, you need to have the sensor replaced, which can cost about $300. .

Read More: Causes And Fixes For A DEF Gauge Not Working

Bottom Line

When your DEF gauge shows empty when full, many things may contribute to this issue. So, it is best to identify the cause of the problem to have it addressed appropriately and prevent further damage from happening.

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