UFA offers on-island Cardlock DEF at 24 locations and counting! What is DEF? DEF, or Diesel Exhaust Fluid, is a clear non-hazardous liquid that works with selective catalytic reduction (SCR) technology to convert harmful nitrogen oxide (NOx) from heavy-duty diesel vehicles into harmless nitrogen (N2) and water. UFA sells the leading brand of high quality DEF, Air1®, which is certified by the API™ to meet ISO 22241 standards for optimal engine performance. Why is Diesel Exhaust Fluid Important? Modern diesel engines use DEF to generate cleaner exhaust and reduce harmful air pollution. In 2010 the Canadian American Environment Protection Agency (CEPA) introduced diesel emission standards that mandate the use of DEF in most commercial-grade diesel engines. Cardlock DEF UFA offers on-island Cardlock DEF at 24 locations and counting, available 24/7. All our Petroleum Agencies and select farm stores also carry various sizes for your carry-out convenience. Find a DEF Cardlock Location near you We have 24 on-island Cardlock DEF locations and counting. Pick one closest to you to learn more about it. Learn More Don't see your town? Check out location finder.