Background - Software Upgrade for Diesel Trucks

This page last reviewed January 9, 2013

History of Software Upgrade for Diesel Trucks Program

This page contains information about the California Air Resources Board's Low NOx Software Upgrade Program.


In the 1990's, engine manufacturers utilized 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 oxides of nitrogen (NOx) emissions during highway driving.  The United States Environmental Protection Agency (U.S. EPA) and ARB consider these strategies to be defeat devices (a.k.a. dual mappign and transient sensing algorithms) that result in off-cycles emissions.

In 1998, the following manufacturers signed Consent Decrees with the U.S.EPA, the Department of Justice (DOJ), and the ARB: Caterpillar, Cummins, Detroit Diesel, Navistar, Mack/Renault, and Volvo. 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 is simply engine software upgrades designed to reduce the increased 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 ten percent of the applicable engines have low NOx rebuild kits installed nationwide instead of the nearly one hundred percent that was expected. Therefore, excess NOx emissions continue to be emitted. In order to reduce NOx emissions, staff has developed a regulation that requires the low NOx engine software upgrade on applicable model year 1993 to 1998 engines.

Voluntary Software Upgrade Program

Board Direction to Staff

At the March 25, 2004, meeting of the Air Resources Board, the Board approved the Voluntary Program for Software Upgrade and the proposed Software Upgrade regulation as a backstop to the Voluntary Program. The Board directed that initial reporting of the Low NOx Rebuild Software installation status should be quarterly. The Board moved up the timeline for 100 percent of the eligible engines to be reflashed - calling for that to happen by 2008 (instead of 2010). The Board also directed staff to convene a Software Upgrade Voluntary Program Coordination Group, which will include environmental representatives, dealers, and other stakeholders interested in tracking the progress of the Voluntary Program.

Interim Update

At the October 28, 2004, meeting of the Air Resources Board, the staff apprised the Board of the interim results of the Voluntary Software Upgrade Program reflash results. Aproximately 15 percent of the eligible engines were reflashed by September 7, 2004. The target for the first phase of the Voluntary Program was 35 percent. The board expressed their desire to wait until the December board meeting to hear the final results for the first phase of the Voluntary Program.

Voluntary Program Continues for Owners of Detroit Diesel Engines<

At the December 9, 2004, meeting of the Air Resources Board, the Board directed staff to file with the Office of Administrative Law (OAL), the regulation approved at the March 25, 20004, board meeting. Approval of the filed regulation by the OAL will cause the regulation to become effective and enforceable.

The Board directed staff to clarify the language of the regulation to protect the vehicles owners from incurring charges for the low NOx software and its installation. The clarifications also ensure that all dealers authorized to install low NOx software will participate by installing the low NOx software.

The regulation applies to low NOx rebuild engines manufactured by Caterpillar, Cummins, Volvo, Mack/Renault, and International. Low NOx rebuild engines manufactured by Detroit Diesel Corportation (DDC) should continue to be reflashed under the Voluntary Software Upgrade Program; however, if reflash progress is not significant, then owners of DDC engines would also be subject to regulation.

The clarifications to the regulatory language were made available to the public for a 15-day comment period.

Software Upgrade for Diesel Trucks Final Rulemaking

The final rulemaking package was approved by OAL on March 21, 2005 and became effective that same day.

Outreach Letters

Letter to International Registration Plan (IRP) Truck Owners / Operators (in English) (pdf - 56 KB)
Letters to Trucker (and Motor Home Owners) (in English) (pdf - 93 KB)
Letters to Trucker (and Motor Home Owners) (in Spanish) (pdf - 30 KB)
Letter to Owners of Medium-Duty Ford Trucks (in English) (pdf - 19 KB)

Litigation Status

Engine Manufacturers Sue

The Engine Manufacturer's Association (EMA) and four engine manufacturers (Caterpillar, Cummins, Mack/Renault, and Volvo) are suing the Air Resources Board alleging lack of authority to adopt the Low NOx Software Upgrade Regulation and that adopting the regulation breaches the Settlement Agreements. A motion for a temporary restraining order (TRO) was denied (February 2006) and the regulations remain in effect. Trial date is set for August 8, 2006.

Regulation Declared Invalid

The Sacramento County Superior Court has ruled that the Low NOx Software Upgrade Regulation is invalid. The ARB is suspending further enforcement of this Regulation pending entry of a formal order and judgment. The Court's ruling does not invalidate the required installation of Low NOx Software at the time of engine rebuild. The ruling also does not invalidate voluntary efforts to reduce NOx emissions through the installation of Low NOx software. The ARB encourages all voluntary efforts to have the software installed.

Voluntary Software Upgrade Program Regulatory Activities