DIESEL EXHAUST FLUID: WHAT IS IT AND WHY YOU SHOULD LET THE PROFESSIONALS HANDLE IT

December 16, 2019

Lori Drouillard

One of the main challenges for drivers who have cars with diesel engines is in knowing that some of maintenance that is performed on it cannot always be DIY. For example, handling the Diesel Exhaust Fluid (DEF or AUS 32) required in diesel engines is better off left to professionals. Professionals can make sure that the DEF being used is of the highest quality. When drivers purchase DEF by themselves or leave it to fill-up locations that don’t identify the manufacturer and brand name on the receipt it can lead to engine damage. And while it may technically be true that some drivers can refill this fluid themselves, this approach is not at all recommended. Let’s take a look at just what DEF is, what it does and why you are better off letting experienced professionals refill it in your car.

What it DEF?

Diesel Exhaust Fluid is a caustic solution, which is 32.5% urea and 67.5% de-ionized water. It is injected into the diesel exhaust stream and the heat from the exhaust, the fluid, and a catalyst convert the Nitric Oxide (NOx) into harmless gases. This is done so that cars and trucks that have diesel engines can meet the U.S. Environmental Protection Agency (EPA) emissions requirements.

Reasons You Should Let Professionals Replace the DEF in your Vehicle

  • Professionals are better able to guarantee that the DEF placed in your car is labeled to comply with ISO (International Organization for Standardization) 22241 specifications. The use of low-quality DEF is detrimental to the life of the selective catalytic reductant system and can also affect your car’s ability to reduce harmful NOx emissions. Moreover, low-quality DEF can lead to catalyst poisoning, deposits, and injector/filter clogging.
  • The fluid is difficult to fill for a layperson. DEF is a hazardous chemical and will crystallize on contact with air. Therefore, it needs the skill of certified mechanics in order to ensure that it is filled properly in your car.
  • Monitoring your car’s DEF levels is done electronically, so you will need to keep an eye on your dashboard for a warning regarding this fluid. Professionals are better able to ensure the fluid is full when filling, as there is no dipstick, keeping you in compliance with emissions regulations. Doing this will also protect your engine from costly repairs in the future.

Some things are better left to the professionals. As experts in import car repair, we use API-licensed Diesel Exhaust Fluid to ensure that the DEF we place in your engine meets the high standards required by engine and vehicle manufacturers. Our  import car service center in Michigan  specializes in all areas of  Mercedes repair in Michigan  as well as Volkswagen, Audi, and other European makes.

By Lori Drouillard April 9, 2026
If your Porsche hesitates between gears, jerks during shifts, slips unexpectedly, or refuses to engage drive or reverse smoothly, the transmission valve body is one of the first places a qualified Porsche specialist checks. Valve body failure is a well-documented issue on Porsche’s PDK and Tiptronic transmission platforms — and it’s a repair that demands […] The post Where To Go in Royal Oak to Tackle Porsche Transmission Valve Body Failure appeared first on Autohaus Service And Sales.
By Lori Drouillard March 13, 2026
If you are driving a Volkswagen, then you know they are engineered for performance, comfort, and innovation. However, like any other car, Volkswagens may encounter problems over time, and one such problem is the failure of the fuel pressure regulators. If you are in the Royal Oak, MI, area and something suspiciously wrong with your […] The post Where Should You Go in Royal Oak To Address Volkswagen Fuel Pressure Regulator Failure appeared first on Autohaus Service And Sales.
By Lori Drouillard February 10, 2026
A high-end car like the Audi signals that you value style, enjoy strong performance, and prefer a vehicle built with high-quality engineering. But even a solid and well-built engine wears down eventually. Whether you are driving through Royal Oak, Michigan (MI), or stuck in heavy traffic, the condition of your engine directly affects your car’s […] The post Top Signs Your Audi Needs Immediate Engine Service in Royal Oak appeared first on Autohaus Service And Sales.
By Lori Drouillard January 17, 2026
When you buy an Audi, you expect superior performance, precise German engineering, high-tech utility, a sleek, luxurious aesthetic, and unparalleled safety. Safety features define the car’s drivability, establishing driver and passenger safety and trust. The brake system is a crucial component, without which the vehicle’s safety is incomplete. Several brake-related malfunctions and issues go unnoticed […] The post Brake Problems Royal Oak Audi Drivers Should Never Ignore appeared first on Autohaus Service And Sales.
By Lori Drouillard December 22, 2025
BMW vehicles are a masterful blend of performance, luxury, and precision engineering. With advanced tech integration, fine-tuned vehicle systems, and superior performance mechanics, the vehicles are testaments to sophisticated engineering, with a very low tolerance for irregularities and malfunctions. That’s why you need certified mechanics with specialized expertise and training in BMW vehicles, ensuring accurate, […] The post What to Look For When Choosing Certified BMW Mechanics appeared first on Autohaus Service And Sales.
By Lori Drouillard November 19, 2025
Owning a Mercedes-Benz is about experiencing the pinnacle of automotive engineering, luxury, and performance. However, to maintain high-quality vehicle performance, you must have Mercedes maintenance services performed. These maintenance services fine-tune the car, remove accumulated debris, and detect and repair malfunctions before they worsen. The Importance of Mercedes Maintenance Autohaus Service and Sales has been […] The post Why Routine Mercedes Maintenance Matters For Royal Oak Drivers appeared first on Autohaus Service And Sales.
By Lori Drouillard October 14, 2025
For Audi owners, the smooth, responsive, and precise handling is an important part of their driving experience. The steering system requires attention to prevent common issues that can compromise the safety and performance. Routine maintenance is crucial in combating wear and tear from daily driving. Specific proactive steps need to be taken, including checking fluid […] The post How Royal Oak Audi Owners Can Prevent Steering Problems appeared first on Autohaus Service And Sales.
By Lori Drouillard September 13, 2025
Is your Volkswagen transmission system due for inspection? If you cannot recall the last time the transmission on your Volkswagen was checked and serviced, it is high time that you did so. Your car’s transmission system is among the most essential parts since it is in charge of moving power from the engine to the […] The post Top 5 Reasons To Prioritize Transmission Service For Your Volkswagen appeared first on Autohaus Service And Sales.
By Lori Drouillard August 13, 2025
Porsche is one of the most sought-after high-end sports cars, evoking awe and envy from passersby and competitors alike. No doubt, buying a Porsche is a proud moment; however, the joy of driving these luxury cars can be short-lived when you encounter issues, especially water pump failure in the case of Porsche. The water pump […] The post What Are Some Tips To Detect Porsche Water Pump Leaks? appeared first on Autohaus Service And Sales.
By Lori Drouillard July 13, 2025
The half-shaft boot is a critical component of the drivetrain that covers the CV joints. To understand the significance of the half-shaft boot, it is crucial to understand the function of the CV joint. The CV joint assists in the transfer of power from the transmission to the wheels. Additionally, it maintains the wheel’s rotation […] The post Tips To Prevent Volkswagen Half-Shaft Boot Failure appeared first on Autohaus Service And Sales.