Written By: Corey Foy

7 Frequently Asked Questions about Diesel Exhaust Fluid (DEF)

The Canadian Environmental Protection Agency (CEPA) and the US Environmental Protection Agency (EPA) have legislated that emissions of NOx from diesel engines be reduced significantly.


The legislated emissions of nitrogen oxide (NOx) have led to the Selective Catalytic Reduction (SCR) technology and Diesel Exhaust Fluid (DEF). We’re here to answer your seven most frequently asked questions about DEF.

1: What is DEF?

DEF is a non-toxic fluid composed of purified water and automotive grade aqueous urea. DEF is available in a variety of storage and dispensing methods. Storage options consist of various size containers such as totes, drums, or jugs.

2: What does DEF do?

DEF is used as a liquid reducing agent in a Selective Catalytic Reduction (SCR) catalyst for emissions control. The SCR technology is designed so that NOx reduction reactions can rapidly take place within the catalyst system, using the ammonia from DEF to covert NOx gases into nitrogen, water, and carbon dioxide.

3: How much DEF will I need?

All heavy duty diesel engines manufactured after Jan 1, 2010 must meet the latest CEPA and EPA emissions standards for particulate matter and nitrogen oxides. Typically the DEF usage on an engine will be 1-4% of the fuel consumption, so for every 100L of diesel used you can expect to use between 1-4 litres of DEF.

4: What percentage of urea is in 49 North Lubricant’s DEF?

Our DEF is a high purity solution of urea in water – 32.5%.

5: What will happen when my truck runs out of DEF?

Due to environmental safety CEPA and EPA have contingency plans to prevent a vehicle running out of DEF. The engine is designed to display warnings on your vehicles dashboard.

“Generally speaking, when the DEF tank level drops below 10% an amber warning lamp will come on, at 5% this lamp starts flashing and below 2.5% a solid amber warning light is displayed.

If the truck is allowed to run out of DEF the engine’s power is reduced, a solid red warning will be displayed and the vehicle speed will be limited to 5 mph until the DEF tank is refilled.”


6: If I switch DEF suppliers do I need to clean out the old fluid?

When switching DEF it is not necessary to flush your vehicle’s system clean of the old DEF (unless the quality of the fluid is causing issues). What is recommended is running that vehicle until the DEF tank is as empty as possible before you replace it with a different brand.

7: Is 49 North Lubricants Diesel Exhaust Fluid API Certified?


API Certification ensures that consumers are able to identify DEF that meets the requirements set by CEPA and EPA and gives you a choice between only high quality brands.


DEF is available for purchasing at various locations, including truck stops, dealerships, engine distributors, and 49 North Lubricants! DEF tanks range in size from 18 to 90 liters depending on the trucks application. The DEF tank fill opening is designed to accommodate a DEF fill nozzle to ensure that only DEF is put in the tank. The cap is also blue in order to differentiate it from the diesel fuel tank.