Exhaust Fluid System Fault? [All You Need To Know]

You’ve found your way here because you are facing some problems with the exhaust fluid system. SCR-equipped vehicles are more likely to receive this alert. 

You might seek the answer of what are the reasons, effects, and solutions.

 So, what are the exhaust fluid system fault?

When the power control module detects a DEF pump, injector, or NOx sensor fault, the engine computer warns. Empty fluid tank, tainted fluid, a faulty sensor, and temp resistance can be the faults. It harms our environment and degrades performance. Proper monitoring and resetting can help.

Well, this was just a glimpse of the information you require. To operate your vehicle properly you will need further information about the exhaust system which this article will provide.

Hope you will stick around.

What is Diesel Exhaust Fuel System?

In simple words what is an exhaust fluid system?  Diesel Exhaust Fluid is pumped into the exhaust stream of diesel automobiles. This is to convert hazardous NOx pollutants into nitrogen and water.

It turns toxic exhaust gasses into non-toxic nitrogen and carbon dioxide. The DEF system was created to safeguard the environment from dangerous fuel by-product emissions. This is a transparent solution made of urea and water (1:2).

The vehicle’s fuel system might be harmed if the DEF system is not maintained.

Manufacturers used Selective Catalytic Reduction (SCR) to meet EPA emissions standards in 2010.

Here we suggest some of the best brands of exhaust fluid you can use.

Why Exhaust System Fault Warnings Occur

Why do Exhaust System Fault warnings appear? Well if the sensor senses there is a problem with the system it notifies the owner with a message. The Exhaust Fluid system includes the DEF fluid, the DEF injector, the DEF pump, and the NOx sensor.

Exhaust Fluid System Fault: Causes and Effect

Let’s explore the reasons responsible for causing faults in the exhaust fluid  system.

Empty Diesel Fluid Tank

The alert will appear if your diesel exhaust fluid tank is empty. Even if the tank isn’t empty, the warning will appear on the screen sometime. It indicates that the DEF is decreasing rapidly.

Contaminated Exhaust Fluid

When contamination occurs, the DEF fault messages increase. Diesel exhaust fluid is a potential source of contamination. The introduction of air or water into the DEF tank has the potential to contaminate the fuel.

This can also occur as a result of incorrect filling. Numerous individuals pump exhaust fluid into their diesel tank. Additionally, they fill the exhaust fluid fuel tank with diesel fuel.

Faulty Sensor

The DEF system is controlled by sensors in the SCR system, which stands for selective catalytic reduction. They cease to function if the sensor detects any fluid problems. This is due to a lack of DEF supply and poor DEF quality. 

The DEF system is controlled by sensors in the SCR system, which stands for selective catalytic reduction. They cease to function if the sensor detects any fluid problems. This is due to a lack of DEF supply and poor DEF quality.

Problems with Tamper Resistance

The exhaust gas temperature (EGT) sensors on the SCR system measure the temperature of the exhaust gas. The sensor alerts the driver if the vehicle becomes excessively warm. The sensor also fails if the temperature is too low.

The exhaust fluid will freeze if the temperature drops too low. Thus, the DEF tank heating system is unable to keep up with demand. Also, the DIC does not have the ability to indicate the DEF level.

Impact of a Fault in the Exhaust Fluid System

Let’s explore the other impacts of an exhaust fluid system failure.

Threat To Environment 

DEF is a non-toxic solvent. It also has 67.5% deionized water and 32.5% urea. This solution is used in diesel exhaust.

Diesel exhaust fluid degrades NOx. Then DEF converts them to nitrogen and water. So, if the Diesel Exhaust Fluid system fails, toxic gas levels will rise in our environment. It will be a threat to all the living creatures.

Limits Speed and Idles Engine

Speed and engine power are limited in a selective catalytic reduction system when DEF alerts are given. The actions the car takes depend on messages from the DIC.

Let’s find out which warning messages do the things that they say.

DIC MessageEffects
In XX miles, speed is limited to 50 mphThe car's top speed will be limited by the distance shown on the screen.
Speed is limited to 50 mph upon restartWhich limits the car's top speed. The restriction begins upon restart.
Speed is limited to 50 mphIt limits the top speed at a certain point.
The engine idled soonThe engine is switched to idle-only mode.

What to Do with Faulty Exhaust System

You need to keep some things in mind while checking the faults in the exhaust system. these can be:

Look for Solutions In the Manual

The first thing to do if you get a DEF warning is to read your manual. The warning notice advises that the owner’s manual should be consulted.

Manual lets you know which warnings mean what. In addition, you’ll learn what the engine will do in response to the signals. It also provides you with a list of potential options.

Checking The Exhaust Fluid System Properly

Before taking your car to a service center do check the Exhaust Fluid tank. It is to see if the fuel is clear in color. If it’s not you will need to flush and refill the tank. This might solve your problem.

Check the Temperature

Exhaust fluid from diesel engines behaves in the same way as water. Low temperatures cause it to freeze. Liquids will freeze at -9° C or lower in the wintertime.

DEF heater is the answer. However, the DEF tank heater may not work. So park your truck in a heated garage. You can also use a heater to warm up the garage.

Resetting Exhaust Fluid System

Even after taking all essential procedures, alerts might appear. In this scenario, you can try resetting the exhaust fluid system. There are two reset options available.

That’s all we had to say.


Is DEF fluid made from urine?

DEF is a mixture of (typically) 2/3 deionized water and 1/3 urea. Technically, urea is derived from one of the byproducts of urine. But it’s synthetically made.

How long can DEF fluid be stored?

DEF has a shelf life because it doesn’t include any preservatives. However, DEF has a long shelf life. Typically, it can be stored for up to a year without any problems.

How many miles can a gallon of DEF be used before running out?

Generally speaking, one gallon of DEF will last between 300 and 500 miles in most DEF tanks. While using 50 gallons of diesel fuel. Keep the DEF tote full so that it doesn’t run out of space.


Hopefully, you found the answer to the reasons, effects, and solutions to exhaust fluid system fault. If you still haven’t found the answer you were looking for please visit the nearest service center.

Thank you and Good Luck!

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