Electrical, Charging & Network fault codes
Charging, grounds and the J1939 network: alternator output, battery and sensor-supply voltage, lighting and starter circuits, and every lost-communication code — whichever module dropped off the bus, a U-code is a network fault and is diagnosed at the datalink. One corroded ground or chafed harness can set half a dozen unrelated codes at once, so read the whole list before replacing anything.
All 30 electrical, charging & network SPN/FMI and OBD codes in the knowledge base are listed below — each with what it means, how serious it is, the most-likely causes, and what to check first.
Electrical, Charging & Network codes (30)
Other systems
Cooling, lubrication, HVAC and chassis/cab codes are listed on the fault code lookup, along with the search box that covers every code.
General diagnostic guidance for heavy-duty diesel equipment (Cummins, Detroit, PACCAR, Volvo, Mack and more). Not a substitute for a scan-tool diagnosis on your specific truck.