The SPN 792 FMI 2 code on your Peterbilt Peterbilt Peterbilt Motors Company is an American truck manufacturer. Established in 1939 from the acquisition of Fageol Truck and Motor Company, Peterbilt specializes in the production of heavy-duty (Class 8) and medium-duty (Classes 5–7) commercial vehicles. https://en.wikipedia.org › wiki › Peterbilt Peterbilt - Wikipedia 579 indicates that the right rear wheel speed sensor is open or shorted. This can cause erratic, intermittent, or incorrect data to be sent to the ABS system, which can lead to a number of problems, including:1. ABS warning light illuminated2.