Know Why DEF Light Blinking On Freightliner Tank Is Full?

Why DEF light blinking on Freightliner tank is full? Though the DEF light blinks mainly when the DEF tank is empty or nearly empty, if the tank is full, you may have other issues like bad metering. 

But sometimes, the DEF light blinks even, the problem might be in the NOX sensors, or SCR.

We have discussed all the reasons why the Freightliner DEF light might be blinking even when the tank is full. 

Causes and Solution to DEF Light Blinking on Freightliner

We understand that you might have the time to go through the entire guide, which is why we designed this table. Go through it, and you will know what to do if the DEF light is blinking.

There is a fault in the gaugeGet the gauge repaired or replaced
Bad DEF meteringInstall a high-quality DEF meter
Issues with the NOX sensorsGet the sensors checked by an expert, then act accordingly
Could be a technical malfunctionA mechanic will do a thorough check to find the issue
Fluid contamination Change the diesel emission fluid immediately

Why does DEF Light Blink When the Tank is Full? 

Many people have asked this question: My DEF tank is full, but why is the DEF light on or blinking? Sometimes the DEF light indeed blinks even when the tank is full. It is tough to find the problem when everything seems alright. 

Most of the time, the reason behind this is the gauge. A faulty gauge can lead to the DEF light blinking. Apart from that, a bad DEF metering system and NOX sensors also can cause the problem. 

We know that a lot on the plate, but since it needs to get fixed, start checking one by one. Once you have ensured that the DEF tank is full, check if the gauge is good. Then check the metering system and NOX sensors.

If everything seems perfect, then it is probably the SCR issue. To find SCR issues, you must attach a scanner, code reader, or any device that can detect malfunction. 

After checking all those mentioned above, if you don’t find any problem, then it is probably the contaminated DEF oil. First, ensure the oil is in good condition; if not, replace the oil with a high-quality one. 

Take your vehicle to an expert mechanic, and they will find the issue by any means. It might cost you a good amount, but that’s worth it. 

What is DEF Light? 

DEF stands for Diesel Exhaust Fluid. And it is a warning light that is supposed to tell the driver that the fluid level is low and you need to refill it as soon as possible. DEF lights have different warning levels; sometimes, it just stays on, and sometimes it blinks. 

4 Levels of DEF Light Warnings 

In this section, we will be looking at 4 levels of DEF lights warning. Check it out. 

1. DEF Light Is On

This is the starter level and is very basic. When the DEF light is on but not blinking, the diesel exhaust fluid level has gone below the established level.

As said before, it is the starter level, you can still ride for a couple of hours with this warning. But if you want the best for your vehicle, especially for your vehicle’s engine, you should refill the tank when you get the chance. 

2. DEF Light Is Blinking 

When you see the DEF light flashing or blinking, that’s telling you that the DEF level is extremely low, and you need to refill now. At this point, you should not ignore this warning because, after this, the engine might stop working.

But if you don’t have the oil near you, in that case, you can drive slightly more after the warning. But don’t take the risk if the DEF fluid store is far; your vehicle might not stay active that long.

3. Blinking DEF Light Along With Engine Check Light On

This is where things start to hurt the engine. When the DEF light is blinking, and the engine check light is on, that means you have completely ignored the past warnings and have to refill the tank. Otherwise, the engine will derate. 

In other words, the engine won’t work until the DEF tank is full. Even after refilling the DEF tank, it might take 10-20 minutes to restore the engine’s normal power. Trust me, when the DEF tank is dry, it hurts the engine, which will be visible after a while.

4. Check The Engine And Stop Engine Light Is On With The Blinking DEF Light

When the stop engine light is on, that means the engine won’t work anymore until you refill the DEF tank. If you have come to this stage, you didn’t care about any previous warnings. 

And the engine couldn’t take any more. Upon refiling, within a few minutes, the engine will start to work, but it will cause the engine to deteriorate faster than it was meant to.

This Video Will Help You Too!

Frequently Asked Questions (FAQs)

What does it mean when my DEF light is flashing?

It means the diesel exhaust fluid level is extremely low. When you see that sign, drop whatever you’re doing and refill the tank.

What causes the DEF light to come on?

The DEF light turns on when the DEF level goes below the threshold.


When you see the DEF light blinking on Freightliner tank is full, visit an expert mechanic to find out the problem. They might require you to leave the vehicle to them for a day or two. But you will get a solution. 

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