EPA in June had updated its guidance for certification of truck engines using SCR to reduce emissions, calling on SCR engine makers to continue developing warning systems that alert drivers when the truck’s DEF tank is nearly empty or filled with a liquid other than DEF. The June guidance, mostly in response to previous claims made by Navistar that SCR technology can be circumvented, also urged OEMs using SCR to research methods that would inhibit tampering with SCR system operation and incorporate further inducements for drivers to comply.

Navistar previously had sued both EPA and CARB over their acceptance of SCR technology without stronger measures to prevent engine operation without DEF or an operational SCR system. The truck maker in 2010 settled both lawsuits by garnering a commitment for further review.

Research cited by Navistar was conducted by EnSight, an independent environmental consulting firm, using two long-haul vehicles and one heavy-duty pickup, all of which used SCR. According to Navistar, EnSight’s research showed that when liquid urea was not present, there was little or no effect on the vehicles’ operations.

However, EPA said in its June guidance that testing of SCR systems had yielded mostly positive results. While the agency said Navistar’s findings arose from intentional attempts to circumvent the SCR system and that the majority of operations using SCR would be in compliance, it encouraged SCR OEMs to look further into methods to impede tampering.

EPA’s guidance was published June 7 in the Federal Register; for more information, visit here.