A new guidance from the U.S. Environmental Protection Agency (EPA) regarding selective catalytic reduction (SCR) engines and the miles and hours a truck can run after the DEF tank runs dry. The updated guidance removes any mention of miles or hours driven on an empty DEF tank, and essentially defers to engine manufacturers to set those limits for maintenance–in particular how long after the DEF tank runs dry that engine performance could begin to decline.

WASHINGTON — In an effort to clear the air on its requirements for selective catalytic reduction (SCR) engines, the U.S. Environmental Protection Agency has issued new guidance on the miles and hours a truck can run after the DEF tank runs dry.

The original guidance from the EPA in February 2009, required engine performance to be degraded after a truck travelled a certain distance with an empty diesel exhaust fluid (DEF) tank.

As part of its lawsuit against the EPA, Navistar said that provision in the 2010 engine rules was essentially a “licence to pollute” and “pollution for convenience.”

Citing the petition for review filed in the U.S. Court of Appeals, the EPA decided to rewrite the provision and issued a letter to engine manufacturers on Dec. 30, 2009.

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