U1255 GMC Code - Lost Communications

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message. These node alive messages are used for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once. The following modules communicate on the class 2 serial data circuit:
- Audio amplifier
- Cellular telephone module w/UV8
- Dash integration module (DIM)
- Digital radio receiver
- Driver door module (DDM)
- Driver door switch assembly (DDSA)
- Electronic brake control module (EBCM)
- Electronic suspension control module (ESC)
- Front passenger door module (FPDM)
- Inflatable restraint sensing and diagnostic module (SDM)

• Loose control module connectors
• Faulty control module
• Control modules poor lectrical connection
• Control Modules harness open or shorted