DEF Tanks & DEF Sensors: What You Need to Know

Diesel exhaust fluid (DEF), also marketed and sold as AdBlue®, is a non-hazardous solution used within a selective catalytic reduction (SCR) system. Diesel vehicle manufacturers rely on SCR systems to help mitigate the environmental impact of diesel emissions as required by law.

A major component of any SCR system is the DEF tank assembly, which includes a specially designed tank and level sensor. The DEF tank assembly stores DEF and supplies it to the SCR system. Continue reading to learn more about DEF and its important role in these systems.

What Is DEF and What Does It Do?

DEF is 32.5% urea, or aqueous ammonia solution, and 67.5% deionized water. This solution works within the SCR system to break down harmful nitric oxide and nitrogen dioxide particles — together known as NOx — within diesel engine exhaust.

This chemical process begins with an injection of DEF into the SCR system of a diesel vehicle. DEF reacts with the NOx gasses to convert the toxic NOx into nitrogen, water and small amounts of carbon dioxide. Not only does this process reduce the amount of harmful emissions produced, it also increases the fuel efficiency of the diesel engine.

In the United States, all heavy- and medium-duty diesel truck engines produced after January 1, 2010, must meet the latest EPA emission standards. This is accomplished through the use of an aftertreatment system, which frequently includes SCR technology that utilizes DEF. In addition, all DEF solutions and products must meet the ISO 22241 standard to ensure effectiveness.

Essential DEF Components for Your SCR System

An SCR system consists of three main components: a DEF supply module or injector, a DEF tank assembly and an SCR catalyst. KUS has been collaborating with global exhaust aftertreatment system integrators, vehicle manufacturers and engine OEMs since 2003 to produce SCR system components that adhere to ISO 22241 standards.

KUS specializes in NOx conversion through its DEF product line, which includes both standard and custom DEF tanks, DEF sending units and other accessories. We manufacture our DEF tank assemblies in-house, allowing us to simultaneously engineer, design and validate all of our products. This, in turn, reduces lead times and minimizes compatibility issues.

What You Need to Know About DEF Tanks

DEF is a safe and nontoxic fluid to handle, but it can corrode certain types of metals. As a result, DEF must be kept in a special tank called a DEF tank. The DEF tank is usually situated next to the diesel fuel tank behind the cab of a vehicle.

What’s the Proper Way to Store DEF?

It’s vital to store DEF correctly to ensure its effectiveness. DEF should not be stored in containers made of carbon steel, copper or alloys containing copper or zinc-coated steels. These products can corrode and contaminate the DEF within, which can compromise the SCR system.

DEF can be stored for up to two years when kept at an ideal temperature around 75 to 77 degrees Fahrenheit. The original production date of your fluid can be found on original product packaging. Freezing and thawing the solution will not damage it, but exposing DEF to direct sunlight or temperatures above 86 degrees Fahrenheit can cause it to degrade significantly faster.

Similar to DEF itself, you should always look for DEF products that are made to the ISO 22241 standards, such as KUS DEF Tanks. Products that do not meet this standard may cause issues or failures with your emissions system.

How Do I Know If My DEF Tank is Close to Empty?

The Environmental Protection Agency (EPA) mandates that all diesel engine manufacturers must include a warning system for the DEF tank, such as gauges on the dashboard, to inform the driver of how much fluid remains in the tank.

In many instances, diesel vehicles feature a warning light that will activate when the DEF tank level drops below 10% and begin flashing when it reaches 5%. When the DEF level drops to 2.5%, the light will be a solid amber color. If the vehicle runs out of DEF, its speed will reduce to 5 mph until the driver refills the tank. It’s important to note that not all manufacturers follow this method.

The DEF level sensor is part of the DEF sending unit and it measures the remaining fluid level in the DEF tank. When the level is low, the DEF level sensor sends a signal to the vehicle’s ECU, which triggers the warning light on the dashboard or panel. However, the DEF sending unit usually has additional functions beyond liquid level measurement. 

What You Need to Know About DEF Senders

The DEF sending unit mounts to the DEF tank. It integrates liquid level and temperature measurement functions, and it also regulates DEF temperature via a heating function that utilizes the engine’s coolant. A urea quality sensor is integrated into the DEF sender to measure DEF concentration. All of these components work together to ensure SCR system efficiency.

While all DEF sending units perform the same essential functions, there are a few customization options that can help increase the performance of the unit based on your usage. These include mounting head options, heating tube body forms, and the type of DEF quality sensor used.

Mounting Head Options

KUS offers three different mounting head options for its DEF sending units. They include:

• Bayonet Mounts, which use a bayonet head that connects to a matching opening and is twisted into place and sealed with an o-ring. It is a versatile mounting option.
• Rubber Head Mounts, which were originally designed for a narrow DEF tank that has a small installation area. These have since become popular with OEMs for mounting DEF senders to all types of DEF tanks due to their ease of installation and sealability.
• Flange and Bolt Mounts, which use bolts or screws for mounting by the flange. This mounting method doesn’t require any specialized installation tools making it an easy choice for those who need a quick and easy installation.

Heating Tube Body Forms

KUS produces five different heating tube body forms that utilize the engine’s coolant to heat cold DEF or thaw frozen DEF to the optimal temperature. These include the following forms:

• Coil
• L-shape
• Paperclip
• Combination
• No Heating

The heating tube body form you choose will depend on the climate in which you operate and the shape and size of the DEF tank. In regions where the climate does not get cool enough for DEF to freeze there is no need for heating coils.

DEF Quality Sensor

All of KUS’ DEF sending units are designed to work with our Ultrasonic Quality Sensor, which accurately monitors DEF concentration and quality. The quality sensor alerts the user if the solution deviates from the acceptable concentration range or if there are any contaminants present in the DEF tank. DEF concentration directly influences SCR system performance.

Not all units come with DEF quality sensors, the DEF Quality Sensor is an optional add-on depending on application. Emission regulations mandate that vehicles must have quality sensors.

Buy Premium Exhaust Aftertreatment System Products From KUS

At KUS, we offer industry-leading exhaust aftertreatment products built to the highest standards. Our engineering and design teams have more than two decades of experience creating premium products designed and manufactured in accordance with ISO 22241 standards. We are certain we can provide a solution for you.

To see our full range of products, visit our online store. You can also contact us for more information on exhaust aftertreatment systems, custom solutions or any of our other product offerings.