However, EPA said in its recent 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, go to www.gpo.gov/fdsys/pkg/FR-2011-06-07/html/2011-13851.htm.