U2125
DTC U2105-U2199
CIRCUIT DESCRIPTION
Modules connected to the GMLAN serial data circuits monitor for serial data communications, during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have programmed information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module. When a message that indicates the availability of the transmitter module is not received, the receiver module sets a DTC 21xx where xx is equal to the 2-digit identification number of the transmitter module.
The DTC descriptors listed below provide a method for determining which module is not communicating. A module with a GMLAN serial data circuit malfunction or which loses power during the 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.
DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC U2105 Lost Communications With Engine Control System
- DTC U2106 Lost Communications With Transmission Control System
- DTC U2107 Lost Communications With Body Control System
- DTC U2108 Lost Communications With ABS/TCS Control System
- DTC U2109 Lost Communications With Powertrain Multiple Control System
- DTC U2111 Lost Communications With Steering Control System
- DTC U2113 Lost Communications With Sensing Diagnostic Module (SDM)
- DTC U2116 Lost Communications With Instrument Panel Cluster (IPC)
- DTC U2122 Lost Communications With Radio
- DTC U2125 Lost Communication With Mobile Communications Control Systems
- DTC U2127 Lost Communications With Front HVAC
- DTC U2137 Lost Communications With Vehicle Theft Deterrent (VTD)
- DTC U2171 Lost Communications With DVD Player
- DTC U2172 Lost Communications With Digital Radio Receiver
When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order:
1. Current DTCs before history DTCs unless told otherwise in the diagnostic table.
2. The DTC which is reported the most times.
This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description. Symptoms - Vehicle
CONDITIONS FOR RUNNING THE DTCs
- Voltage supplied to the modules is in the normal operating voltage range.
- The vehicle power mode requires serial data communication to occur.
- DTC U2100 does not have a current status.
CONDITIONS FOR SETTING THE DTC
A supervised periodic message that includes the transmitter module availability has not been received.
ACTION TAKEN WHEN THE DTC SETS
The module uses a default value for the missing parameter.
CONDITIONS FOR CLEARING THE DTC
- A current DTC clears when the malfunction is no longer present.
- A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
DIAGNOSTIC AIDS
- A poor connection at the inoperative module may cause this code to set.
- An improperly powered module may cause this code to set.
TEST DESCRIPTION
Step 1 - Step 11:
Step 12 - Step 14:
The numbers below refer to the step numbers on the diagnostic table:
3. Non ABS equipped vehicles may set a DTC U2108 falsely. If this is the case there is no malfunction with this system.
5. If the body control module (BCM) will not power up, the vehicle cannot establish the correct power mode. This step test for the correct power supply conditions for the BCM.
6. If DTC U2105 to U2177 are set as history and you can communicate with the suspect module, the malfunction is an intermittent communication buss, power supply, ground or internal module connection.
7. This step tests for the correct power supply conditions of the suspect module or modules.
8. This step identifies which of the GMLAN busses the module or modules use for communication.
13. The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
14. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.