What is SCR?

The way SCR works is simple. When engine exhaust gas travels toward the SCR system, it is injected with Diesel Exhaust Fluid (DEF), through a chemical process, ammonia is extracted from the DEF. Ammonia travels with the NOx (in the exhaust gas) towards the SCR canister, where both elements react over the surface of the SCR catalyst. That reaction breaks the NOx emissions down into harmless nitrogen and water vapor— pure, natural components of the air we breathe. The nitrogen and water vapor then pass harmlessly through the tailpipe. SCR is clean, uncomplicated— and frankly, no big deal. Better. SCR.

  • Routine maintenance on the SCR system only requires replacing the DEF filter every 200,000 miles. The SCR system will not change your current maintenance routine- your oil filter, fuel filter, coolant filter and other scheduled maintenance will go on as usual.
  • Blue Bird’s standard 15-gallon DEF tank is the largest DEF tank offered. Our standard 15-gallon tanks offer DEF refills to be timed with regular maintenance intervals— an exclusive Blue Bird feature.


DEF is a benign, noncorrosive, nonhazardous, nontoxic, nonpolluting and nonflammable solution of 32.5% urea and 67.5% purified water.

  • DEF is already widely used in industry, agriculture and many brands of North American trucks. And contrary to competitor reporting, DEF is completely safe and does not become toxic at any temperature.
  • With a majority of the industry actively utilizing SCR technology, the message is loud and clear: Time-tested SCR technology is clearly the best choice for 2010 emissions standards. Better. SCR.