DTC U1000 & DTC U1255: Class 2 Communication Malfunction: Description

Modules are connected to class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among modules. When a module receives a message for a critical operating parameter, module records identification number of module which sent message for State Of Health (SOH) monitoring. A critical operating parameter is one which, when not received, requires that module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within about five seconds of beginning serial data communication, DTC U1000 and/or U1255 is set. When more than one critical parameter does not have an identification number associated with it, DTC will only be reported once.

Conditions for running DTC U1000 and U1225, voltage supplied to affected module is within normal operating voltage range (about 9-16 volts). DTCs U1300, U1301 and U1305 are not currently set. Vehicle power mode (ignition switch position) requires serial data communication to occur. Conditions for setting these DTCs is that at least one critical operating parameter has not been associated with an identification number within about five seconds after beginning serial data communication. When DTC is stored in memory, modules use a default value for missing parameter(s).