Diagnostic Aids

DTC does not normally represent a failure within module. When loss of class 2 serial data communication DTCs ("U" type) are stored as history DTCs, check all possible serial data history DTCs set in each module before diagnosing serial data line. If DTC U1255 is stored in module memory, check for same DTC stored in other modules capable of storing this DTC. Check Data Link Connector (DLC) circuit to determine which modules may set DTC U1255. See appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS. If DTC is set as a history DTC, problem is intermittent.