This service manual provides information for troubleshooting and servicing generator sets with PowerCommand 2100 controllers. It covers generator set models DGBB through DGFC with specifications A through V. The manual contains sections on control operation, circuit boards and modules, troubleshooting, power transfer control troubleshooting, control adjustment and service, servicing the generator, fuel transfer pump and control, and wiring diagrams. It is intended to assist technicians in maintaining and repairing these generator sets.