Claiming that the “issues” that had predicated it filing a lawsuit against the California Air Resources Board (CARB) had been addressed by CARB, Navistar International Corp. today withdrew that suit.

Navistar said it had sought a ruling in a San Francisco Superior Court declaring that CARB was improperly certifying 2010 diesel engines equipped with SCR (selective catalytic reduction) aftertreatment systems to control emissions of oxides of nitrogen (NOx). “The lawsuit charged that CARB was applying certification requirements which permitted SCR-equipped diesel powered trucks to operate for extended periods without any control of NOx emissions,” said the truck and engine maker.

Those requirements, Navistar noted, were contained in “2009 guidance documents” on SCR functionality released by the U.S. Environmental Protection Agency’s (EPA). The Navistar lawsuit also charged the requirements had been adopted by CARB.

Despite dropping the CARB suit, the OEM also stated today that its “separate court action” challenging the EPA’s 2009 guidance in federal court is still pending.

Navistar is the sole U.S. heavy-duty manufacturer to reject the SCR approach, and instead has committed to meeting the rule's standards using high levels of EGR (exhaust gas recirculation). The company is at least initially also relying on emissions credits it has earned with cleaner light-duty diesels produced earlier to 2010 certify engines at a 0.5 g/bhp.-hr NOx level.

Federal court papers filed by Navistar last June argue that EPA has” illegally accommodated the SCR Manufacturers outside of the public eye and allowed them to deploy an emissions control technology that can only be implemented with a de facto and illegal relaxation of the NOx emission standard."

What’s more, Navistar had contended in its initial court motion that EPA's SCR guidance should have been subject to an official rulemaking process and that a required ramp-down process to disable a truck in steps if it is run without the diesel emissions fluid (DEF) needed by SCR would allow those systems to exceed the 0.2 g NOx limit for some period.

According to Navistar, it dismissed the California lawsuit after reaching agreement with CARB “in which CARB agreed that the 2009 guidance documents are not its policy.” Further, said the OEM, CARB agreed to convene a public workshop no later than August to address the issues Navistar had raised.

Navistar stated it “expects the workshop to produce an outcome that will eliminate the opportunity for SCR-equipped trucks to operate with uncontrolled NOx emissions for multiple and lengthy periods of time.”

“We are pleased that CARB is taking this action and we look forward to participating in the workshop,” said Jack Allen, president of Navistar’s North American Truck Group. “We expect that our agreement with CARB will result in equal enforcement of the 2010 NOx requirements for all engine makers.”

FleetOwner has not yet received a response from CARB regarding our questions about the Navistar announcement.