Air Resources Board proposes low NOx software upgrade

| 8/26/2003

The California Air Resources Board is proposing a regulation to require a heavy-duty diesel engine software upgrade for 1993 to 1998 engines.

In the 1990s, engine manufacturers used computer-based strategies on engines in trucks, school buses, urban buses and motor homes that allowed the engines to comply with emission limits under certification conditions but also allowed increased NOx emissions during highway driving. The U.S. Environmental Protection Agency and ARB consider those to be defeat devices that result in off-cycle emissions.

In 1998, Caterpillar, Cummins, Detroit Diesel, Navistar, Mack/Renault and Volvo signed consent decrees with the EPA, the Department of Justice and the ARB. The consent decrees stipulate penalties, additional certification requirements, the Low NOx Rebuild Program, an October 2002 deadline for meeting 2004 model year standards, in-use testing, and offset and incentive programs.

The Low NOx Rebuild Program contained in the consent decrees consists of engine software upgrades designed to reduce NOx emissions.

The consent decrees require low NOx rebuild kits to be installed at the time of normal engine rebuild, typically around 200,000 to 300,000 miles of service. However, less than 4 percent of the applicable engines have low NOx rebuild kits installed; nearly 100 percent was expected.

In order to reduce NOx emissions, ARB is developing a proposal that would require the low NOx engine software upgrade on all applicable model year 1993 to 1998 engines.

For a list of engines for which low NOx software is available, visit For general information, call ARB's toll-free number, 1-800-END-SMOG (1-800-363-7664) in California, or 1-800-242-4450.