Software Upgrade for Diesel Trucks

This page last reviewed April 15, 2010

What is Low NOx Software Upgrade?

Low NOx software upgrade is computer programming for electronic control modules in certain heavy-duty engines that reduces excess emissions of oxides of nitrogen (NOx). Owners of most 1993-1998 model year California registered heavy-duty trucks, school buses, and motor homes, and interstate vehicles that visit California, with engines manufactured by Caterpillar, Cummins, Detroit Diesel Corporation, Mack/Renault, Volvo and International can reduce the emissions of their vehicles by having low NOx software installed. When installed, the low NOx software reduces NOx, a component of smog that can damage lungs.

Installing Low NOx Software

  • If you have a 1993 - 1998 model year heavy-duty diesel engine, review the list of engines to determine if your engine is eligible for low NOx software.
  • If your engine is eligible for low NOx software (i.e. on the list of engines), you are encouraged to install the low NOx software.

Low NOx Software Upgrade Status (posted January 9, 2007)

Regulation Declared Invalid
The Sacramento County Superior Court has ruled that the Low NOx Software Upgrade Regulation is invalid. The ARB will not appeal that ruling and is suspending further enforcement of this Regulation. 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 preclude voluntary efforts to reduce NOx emissions through the installation of low NOx software. The ARB encourages all voluntary efforts to have the software installed.

Manufacturers Will Continue to Provide Low NOx Software at No Charge
Engine manufacturers will continue to provide eligible truck owners in California with reflashes upon request. Specifically, engine manufacturers, working through their authorized dealers, distributors and repair facilities, will continue to make available and install at no charge "Low NOx Rebuild Kits" in all covered "Low NOx Rebuild Engines" whenever requested or agreed to by any owner/operator of any reflashable vehicle in California, not just at the time of engine rebuild. ARB acknowledges and appreciates the engine manufacturers' willingness to go beyond that which otherwise is required of them.

Fines Collected for Low NOx Software will be Reimbursed
ARB is also reimbursing truck owners/operators for fines that ARB collected for not having the Low NOx Software installed. ARB is in the process of
determining an appropriate procedure for refunding payments, and will notify owners/operators due for reimbursement by letter as soon as the procedure is established.

Low NOx Software Upgrade Program 2007 Frequently Asked Questions (posted January 9, 2007)

Historic Software Upgrade for Diesel Trucks Program

Authorized Dealers Eligible Engine List Background Voluntary Program
Regulatory Activities