Expand To Show Full Article
Exhaust Fluid System Fault; What It Means & What To Do?

Exhaust Fluid System Fault; What It Means & What To Do?

You are here because you received a faulty exhaust fluid system warning. Vehicles with the selective catalytic reduction system often face this warning. Are you wondering what it means and what you can do about it?

Your engine computer shows exhaust fluid system fault warnings when the power control module finds fault in the DEF pump & injector or NOx sensor. The faults indicate an empty fluid tank, contaminated fluid, or anti-tamper problems. Rechecking exhaust fluid conditions & resetting the engine system is the solution. 

Don’t panic if you see a DEF (Diesel Exhaust Fluid) warning. In this article, we will discuss why your car shows this massage. Also, we will explore how you can resolve this problem.

Overview Of Faulty Exhaust Fluid System

Cause  Effect  Solution 
  • Empty diesel exhaust fluid tank
  • Contaminated diesel exhaust fluid
  • Oxides of nitrogen sensor fault
  • Anti-tamper problem 
  • Engine stops working 
  • Continuous warning messages 
  • Diesel exhaust fluid got frozen  
  • Limited speed 
  • Engine got idled 
  • Refill the diesel exhaust fluid tank
  • Flush the contaminated diesel exhaust fluid
  • Reset the engine system 
  • Change the temperature environment 
  • Go to the service center 

Reasons Behind DEF System Fault Warnings 

Your engine computer displays DEF system fault warnings when it feels there is a fault in the DEF system. DEF fluid, DEF injector, DEF pump, and NOx sensor are the parts of the DEF system. 

Let’s see which causes are responsible for these diesel exhaust fluid warnings.

Empty DEF Tank

If your diesel exhaust fluid tank is empty, it will show the warning. Sometimes, it shows the message even if the tank is not empty. That means the DEF level is decreasing fast.

Polluted Exhaust Fluid 

The DEF fault messages rise when contamination happens. Diesel exhaust fluid is susceptible. Insertion of air or water in the DEF tank can pollute the fuel. 

This also happens because of the wrong refill. Many people pour exhaust fluid into the diesel tank. Also, they pour diesel fuel into the exhaust fluid fuel tank. 

Sensor Fault 

Selective catalytic reduction or SCR system uses sensors to control the DEF system. If the sensor feels any problem with the fluid, they stop working. Inadequate DEF supply and low DEF quality are responsible for this.

Anti-Tamper Problem

SCR system has exhaust gas temperature (EGT) sensors. If the car gets overheated, the sensor sends a warning. Also, if the temperature is too low, the sensor collapses. 

If the temperature gets too low, the exhaust fluid tends to freeze. As a result, the DEF tank heater can not provide enough heat. Also, the DIC cannot mark the DEF level. 

Other Reasons 

The reasons depend on the operating situation of the diesel engine. All the messages fall under the reasons we have already discussed. Hence, we are specifically showing which message refers to which problem. 

DIC Message Causes 
Service Emission System (Not-Tamper)
  • Emission Control fault
  • Interrupted DEF system 
Service Exhaust Fluid System (Tamper)
  • Tampering with the system
Exhaust Fluid Range X MI (KM)
  • Remaining gas less than 1000 miles 
  • Faulty DEF mileage countdown
Exhaust Fluid Quality Poor
  • Poor quality of DEF
  • Hardware reflects poor quality

Effects Of Exhaust Fluid System Fault

The SCR system works as a vein in modern cars, especially in a super-duty truck. Additionally, exhaust fluid works as blood. So, if the DEF system gets defected, the engine collapse. 

Let’s see what other effects a faulty exhaust fluid system has. 

Threat To Environment 

Diesel exhaust fluid is a non-toxic solution. Also, it contains 67.5 percent de-ionized water and 32.5 percent urea. This solution is inserted into the exhaust stream in diesel vehicles. 

Diesel exhaust fluid breaks down toxic NOx emissions. Then DEF turns those toxic gases into safe nitrogen and water. So, if DEF collapses, the toxic gas will increase. 

Limited Speed And Idle Engine 

In a selective catalytic reduction system, the speed and engine power are limited for DEF warnings. The actions the vehicle takes depend on DIC messages. 

Let’s see which warning messages take which actions. 

DIC Message Effects 
In xx miles, speed limited to 50 mph
  • The car’s top speed will become limited in the displayed distance.
  • It starts at 50 miles (80 km).
  • Then the countdown starts.
Speed limited to 50 mph upon restart
  • The car’s top speed will become limited 
  • The limitation starts upon restarting.
Speed limited to 50 mph
  • The vehicle’s top speed gets limited.
Engine idled soon
  • The engine enters into an idle-only mode.
Engine idled
  • The engine will enter into an idle-only mode.
  • The process starts eventually.

Solutions To Faulty Exhaust Fluid System 

See Manual 

When you face Any DEF warning, the first thing to do is read your manual. Even the warning message itself says to see the owner’s manual. 

The manual tells you which warning indicates which cause. Also, you will find what action the engine will take regarding the signs. It gives you the possible solutions too. 

The diesel exhaust fluid fault message depends on the vehicle’s model and brand. We will see what a Ford truck manual shares. Also, you can check the details on the Ford service content on their website. 

Warning Messages  Automatic Effects  Action Required 
In xx miles, speed limited to 50 mph
  • The car’s top speed will become limited in the displayed distance.
  • Refer to the diesel supplement.
  • Check the system by an authorized dealer.  
Speed limited to 50 mph upon restart
  • The car’s top speed will become limited upon restarting
Speed limited to 50 mph 
  • The vehicle’s top speed gets limited.
Engine idled soon  
  • The engine enters into an idle-only mode.
Engine idled 
  • The engine will enter into an idle-only mode eventually.

Check The Exhaust Fluid Fuel System 

Before taking your truck to the service center, check the DEF tank. The exhaust fuel is clear in color. You need to flush and refill the tank if-

  • The fluid changes color 
  • The fluid is milky 
  • The fluid is dense
  • The fluid is polluted 
  • The DEF level is low 
  • The fluid mixes with water
  • Air inserts the tank 

Check The Temperature

Diesel exhaust fluid behaves like water. It gets frozen at a low temperature. If the temperature becomes -9° C or less in winter, it will freeze the liquid. The message will be displayed even after the tank is full.

DEF heater is the solution here. But, the DEF tank heater can fail to heat the fuel tank. You should keep your truck in a heated garage then. Also, you can use a heater to increase the garage’s temperature.

Reset Exhaust Fluid System

Sometimes after taking all the necessary steps, the warnings still shows. In this case, you have to reset the exhaust fluid system. We have two resetting options

One is stationary reset, and another is engine computer reset. Let’s see how to perform them. 

How To Perform Stationary Reset

How To Reset Engine Computer 

  • Loosen the lock nut of the connector of the negative battery cable.
  • Wait for 20 to 30 minutes. Let the engine computer be drained out.
  • Make sure it is completely out of power. It will start to reset automatically.
  • Properly connect and tighten the nut you loosened earlier.

People Often Ask 

What Is The Reason For DEF Consumption?

Low-quality nitrogen oxide or fertilizer urea causes trouble in the Selective Catalytic Reduction system. It increases DEF consumption and system failure.

How To Identify The DEF Tank? 

The diesel fuel tank and exhaust fluid tank are separated in diesel vehicles. The DEF fuel tank is blue in color. At least the cap is blue. It is also known as blue DEF.

Does DEF Cause A Check Engine Light?

Yes, it does. If the diesel exhaust fluid is low in level, it can intricate engine light. The diesel particulate filter triggers the check engine light due to low DEF.

Can I DIY Clean A DEF Dosing Valve?

Yes, you can. You need to manage some primary hand tools to clean the DEF dosing valve. However, you can clean it with a brass bristled brush.

How Can A DEF Pump Fail?

A diesel exhaust fluid pump can fail due to contamination. Dirt, tank scale, and rust are responsible for this. Try to avoid reusing disposable DEF containers. 

Have You Found Your Answer? 

Most super-duty vehicles now have a selective catalytic reduction system. The diesel exhaust fluid turns toxic gases into nitrogen and water in this system. When the engine indicates any fault in the DEF system, it shows warnings. 

A faulty exhaust fluid system means a DEF pump & injector or NOx sensor fault. Check your exhaust fluid tank or DEF tank first. If it’s empty, refill it. Also, if the fluid is contaminated, change it as soon as possible. 

However, resetting your engine system is the ultimate solution. Read our article. It will help you to understand the reasons behind the DEF system-related warnings. You will be able to solve the problem as well.


Related Post: