Data Link Communications

CIRCUIT DESCRIPTION
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 for State of Health monitoring (node alive messages). 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 five seconds of beginning serial data communication, DTC U1000 is set. When more than one critical parameter does not have an identification number associated with if the DTC will only be reported once.

CONDITIONS FOR RUNNING THE DTC
^ The following diagnostic trouble codes do not have a current status:
- B1327
- B1328
- U1300
- U1301
- U1305
^ The vehicle power mode (ignition switch position) requires serial data communication to occur.

CONDITIONS FOR SETTING THE DTC
At least one critical operating parameter has not been associated with an identification number within about five seconds after beginning serial data communication.

ACTION TAKEN WHEN THE DTC SETS
The module uses a default value for the missing parameter.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A current U1000 DTC will clear when all critical operating parameters for the module have been associated with an identification number or at the end of the current ignition cycle.
^ A history U1000 DTC will clear upon receipt of a scan tool Clear DTCs command.

DIAGNOSTIC AIDS
When a malfunction (such as an open fuse to a module) occurs while modules are communicating, a Loss of XXX Communication DTC is set current. When the modules stop communicating (ignition is turned off) the current Loss of XXX Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so a U1000 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only a U1000 is set.

TEST DESCRIPTION

Steps 1-12:

Steps 13-14:

The numbers below refer to the step numbers on the diagnostic table.
1. A Loss of XXX Communication DTC (U1001 - U1254) with a history status may indicate the cause of U1000.
2. The modules not communicating is the likely cause of a U1000 DTC. The modules the following modules communicate on the class 2 serial data circuit:
^ Audio Amplifier
^ Cellular Telephone Module W/UV8
^ Dash Integration Module (DIM)
^ Driver Door Module (DDM)
^ Driver Door Switch Assembly (DDSA)
^ Electronic Brake Control Module (EBCM)
^ Electronic Suspension Control (ESC) Module
^ Front Passenger Door Module (FPDM)
^ Inflatable Restraint Sensing and Diagnostic Module (SDM)
^ Instrument Panel Cluster (IPC)
^ Instrument Panel Integration Module (IPM)
^ HVAC Control Module - Auxiliary
^ Left Middle Door Module (LMDM) W/V4U
^ Left Rear Door Module (LRDM)
^ Memory Seat Module (MSM) W/A45
^ Navigation Data Processor W/UY4
^ Navigation Display Head W/UY4
^ Powertrain Control Module (PCM)
^ Radio
^ Rear Integration Module (RIM)
^ Remote Control Door Lock Receiver (RCDLR)
^ Right Middle Door Module (RMDM) W/V4U
^ Right Rear Door Module (RRDM)
^ Steering Column Module W/N37
^ Theft Deterrent Control Module
^ Window Switch - Passenger Front W/armored car
^ Vehicle Interface Unit (VIU) W/UE1

7. The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set Loss of XXX Communication DTCs (U1001 - U1254) for those modules that it was monitoring.
9. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
11. If all modules are communicating, the module which set U1000 DTC may have done so due to some other condition.
12. The module which set the U1000 is the likely cause of the malfunction.

"For the description of RPO code(s) shown in this article or any of the images therein, refer to the RPO code list found at the Vehicle/Application And ID." RPO Codes