DTC U1000: Class II Communication Malfunction: Notes

Modules connected to the Class II Serial data circuit monitor for serial data communication during normal vehicle operation. Operation 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 for State of Health (SOH) 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 about 5 seconds of beginning serial data communication, DTC U 1000 is set. When more than one critical parameter does not have an identification number associated with it, the DTC U1000 will only be reported once. DTC U1000 will set as long as U1300 or U1301 do not have a current status.