DTC U1001-U1254: Loss Of XXX Communications: Description

Class 2 serial data link is used to communicate information and commands between modules. When a module receives a message for a critical operating parameter, the module records the ID number of the module which sent the message for "state of health" monitoring (NODE ALIVE messages). A critical operating parameter is one which, when not received, requires that module to use a default value for that parameter. Once an ID number is learned by a module, it will monitor for that module's NODE ALIVE message. Each module on class 2 serial data link is required to send a NODE ALIVE message every 2 seconds. When no NODE ALIVE message is detected from a learned ID number for 5 seconds, DTC U1XXX (XXX is equal to the 3-digit identification number) will set. To determine which system is not communicating, see MODULE DTC IDENTIFICATION  table. For example, if DTC U1016 is set, Powertrain Control Module (PCM) is not communicating. A module with a class 2 serial data link malfunction or which loses power during a current ignition cycle will have a loss of communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that cannot communicate.

If more than one loss of communication DTC is set in either one or multiple modules, perform diagnosis in the following order:

• Current DTCs before history DTCs, unless otherwise instructed in testing procedure.
• DTC which is reported the most times.
• From lowest number DTC to highest number DTC.

Current DTC U1001-U1254 will clear when NODE ALIVE message from the failed identification number is detected on class 2 serial data link or at the end of the current ignition cycle. A history DTC U1001-U1254 will clear after 50 consecutive ignition cycles if conditions for setting DTC are no longer present.