The California Air Resources Board (CARB) has reviewed the results of a DF test
program conducted by the Truck and Engine Manufacturers Association (EMA.) The
results showed that while engine out emissions for SCR equipped engines were
predictable and consistent, actual tailpipe out emission levels were higher at the end of
Useful Life (UL) when compared to emission levels extrapolated to UL from lower
service accumulation points (35%, 50% or 75% UL). CARB has also been analyzing
base-line test results provided by manufacturers as part of On-Board Diagnostics (OBD)
Manufacturers Self Testing (MST) requirements for on-road heavy-duty engines. A
significant number of engines and after-treatment systems (ATS) tested at 70-80% UL
have been failing applicable certification standards.
