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Close-up of a car’s exhaust fluid tank with a bright blue cap, with the caption “How to Check Your Diesel’s Exhaust Fluid Level”

Almost all diesel-powered vehicles built since 2010 require the use of Diesel Exhaust Fluid (DEF). DEF is made from pure urea and de-ionized water, is a non-toxic, colorless, odorless, and non-flammable fluid. DEF is responsible for moderating your vehicle’s emissions and meeting EPA guidelines. DEF is required for a process known as selective catalytic reduction. This process works by diverting your diesel’s exhaust gases through a filter and then into a catalyst. The gases mix with the DEF which turns hazard emissions into a harmless combination of water and nitrogen. As with all other vehicle fluids, monitoring the DEF levels should be part of your vehicle’s ongoing maintenance. Here is a quick guide on everything you need to know about checking your diesel’s exhaust fluid level.

  • Checking the DEF Levels. DEF is stored in a tank on board the vehicle and injected into the exhaust system. The storage tank is usually found either next to the diesel fuel tank on a truck, or near the area of the spare tire on a car. All vehicles with diesel engines meeting 2010 or later EPA guidelines have a dashboard warning system that alerts you when the DEF level is low.
  • Topping Off the DEF. Adding more DEF is easy since it can be found in all truck stops and automotive parts stores. You can also find DEF at major OEM locations and distributor locations. As of 2013, some truck stops added DEF pumps next to the fuel pumps so that you can fill up both fluids without moving your truck. Even if a level check doesn’t indicate that DEF is low, it is good practice to fill up before long trips to avoid any problems.
  • Amount of DEF Your Diesel Uses. DEF consumption can vary based on environmental factors but is normally expected to be between 2 and 3 percent of fuel consumption. This means that for a diesel truck with a 36-gallon gas tank, around 1 gallon of DEF will be used for every full tank of gas. Two common factors that contribute to DEF consumption percentage are the vehicle’s intended usage, and geographical elements like type of terrain.
  • Shelf Life of Diesel Exhaust Fluid. The shelf life of DEF is a function of ambient storage temperature. DEF can last for about 2 years if the maximum storage temperature does not exceed 75 degrees Fahrenheit for any extended amount of time. DEF that is purchased at an auto parts supply store or truck stop should have an expiration date.

Checking and topping off your diesel’s exhaust fluid level is a simple but important part of your routine vehicle maintenance. If your diesel runs completely out of DEF, a red warning indicator will light up and the vehicle’s speed will be drastically reduced. Once you turn the engine off, your vehicle will not re-start without any DEF, and you could be left stranded.

For any and all diesel repair needs in the Meridian, Idaho area, come to Gem State Diesel. We are committed to customer satisfaction and offer a 24-month, 24,000-mile guarantee for our repair services. Call us at 208-288-5555 or visit us online to set up an appointment today.