CHICAGO -- Anyone who wondered whether Navistar is satisfied with the EPA's recent announcement to impose tougher standards on rival SCR engine suppliers, now have their answer:

Nope.

After dropping a previous court challenge against EPA last year (when the agency agreed to hold public hearings to address Navistar's concerns with SCR engines) the Illinois-based truck and engine maker filed another lawsuit on July 5 and once again accused the EPA of allowing competitors to circumvent the 2010 emission rules.

"It’s about a level playing field," Navistar Spokesperson told the Springfield Sun News.

Ever since it decided not to purse SCR to meet the '10 rules, Navistar has claimed the requirement to use urea-based DEF aftertreatment (diesel exhaust fluid) to eliminate NOx, creates "compliance loopholes."

It argues that drivers could defeat the emissions standards by theoretically forgetting or refusing to fill the DEF or substituting it with a cheaper substance or even plain water.

It has even pushed for the recall of SCR engines. 

Navistar's latest suit, filed in the U.S. District Court for the District of Columbia, alleges that the EPA certified SCR systems without taking those factors into account.

"(DEF) fill-ups are both expensive and inconvenient for the customers of SCR engine makers," the suit states, adding that when the DEF tank runs empty NOx emissions can rise considerably.

"As a result, EPA unlawfully and preferentially helped (and intends to continue to help) SCR engine manufactures by making it easier for them to compete with other emission control technologies by reducing or eliminating the need for drivers to refill with DEF, which in turn allows SCR engines to become heavy polluters above the lawful emission standards."

Last month, however, the EPA acknowledged some of those concerns and announced a proposal that would increase safeguards to ensure drivers fill or replenish DEF tanks. The proposal also calls for better warning systems to identify and respond to low levels or poor-quality DEF and have better tamper resistance, among other improvements. 

Though, the EPA did dismiss Navistar's claim that its rivals' SCR engine systems are routinely tricked and bypass the 2010 emissions regulation. It said the overwhelming majority of drivers comply with the DEF requirement and Navistar's allegations are "clearly not representative of the vast majority of truck operations."

It now appears, then, that Navistar was hoping for a much bolder move from EPA.