Keeping Your Diesel Pickup and SUV Exhaust Clean: It’s as Easy as abc…DEF!


As you’re probably aware, the latest model diesel automobile engines run just as clean, or cleaner, than their gasoline counterparts. And for this, you can thank your trusty blue-capped tank of


. Now DEF stands for…Diesel Exhaust Fuel.

DEF is a non-toxic solution – de-ionized water with 32.5% urea, to be exact – that gets sprayed into the exhaust stream exiting your vehicle. DEF reacts with the exhaust by breaking down dangerous NOx, or nitrogen oxides, into harmless nitrogen and water

The system that handles this process, called Selective Catalytic Reduction (SCR) is found in a large number of diesel pickups and SUVs. DEF only comes into contact with diesel exhaust that is on its way out of the vehicle. It is not a fuel additive. A separate tank stores DEF, and this tank typically has a blue filler cap.

DEF Maintenance

The good news for drivers who prefer smooth, easy maintenance, is that you basically can’t run out of DEF!…Or rather, you can’t run out of DEF in a way that will cause any type of damage – whether to your vehicle OR the environment.

Because of the importance of DEF in generating clean exhaust, the EPA requires that diesel engines be designed such that they cannot run without DEF. As a result, the driver typically will get a series of increasing alerts as the DEF tank runs down. When the tank level drops below 10%, an amber warning light appears; below 5%, the lamp begins to flash; and below 2.5%, the light becomes solid.

If you do happen to completely run out of DEF, you’ll have some extra time to think about it!…As your engine power will likely be automatically reduced to a 5 mph level, and you will see a solid red warning light.

No worries, however, as you simply need to add DEF to the tank.

If you are adding the solution yourself, keep in mind:

* DEF does have a 

Shelf Life

 and will come with an expiration date on any packaging. While not as limited as dairy products! – typical DEF shelf life is about two years – exposure to sunlight, or to warm temperatures for extended periods of time, can considerably reduce the shelf life.

* DEF is also 


 to some metals. While overall, DEF is actually the least hazardous fluid in your vehicle, it is corrosive for some metals. You can obtain more information on the properties of DEF from the supplier.