DTC U1XXX: Lost Communication With XXX: Description

Modules connected by class 2 serial data circuit monitor communications during normal vehicle operation. Operating information and commands are exchanged between modules. When a module receives a message for a critical operating parameter, receiving module records identification number of sending module for state of health monitoring (node alive messages). Critical operating parameter, if not received, requires receiving module to use default values for that parameter. Once a identification number is learned by a module, module will monitor for that modules node alive signal. Each module on class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a node alive signal every 2 seconds. If a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, a DTC U1XXX (XXX equal to 3-digit identification number) will set.

Control module ID number list identifies which module is not communicating. See MODULE IDENTIFICATION  table. A module with internal class 2 serial data circuit malfunction or which loses power during current ignition cycle would have a lost communication DTC set by other modules. Modules that can communicate will set DTC indicating the module that cannot communicate. When node alive signal is not detected from a learned identification number for 5 seconds, a DTC U1XXX will set. When more than one loss of communication DTC is set in either one module or several modules, diagnose current DTCs before history DTCs, unless directed otherwise in testing, DTC which was reported the most times and then from lowest number DTC to highest DTC.