Reflashing involves reconfiguring the engine control chip with new software that recalibrates the tractor engine. This recalibration is meant to lower nitrogen oxide (NOx) emissions by slightly modifying the combustion parameters within the engine. This strategy applies to certain engines built by seven different engine manufacturers (Caterpillar, Cummins, Detroit Diesel, Mack, Renault, Navistar/International & Volvo) between the years of 1993 and 1998. Please note that as of March 2004, the California Air Resources Board (CARB) has mandated the reflashing of medium and heavy duty diesel vehicles in the state of California, on a phase-in schedule, at no extra cost to the vehicle owner. For more information, please refer to the CARB rule at http://www.arb.ca.gov/regact/chip04/chip04.htm.