Circuit Description
Modules connected to the GMLAN serial data circuit monitor for serial data
communications on the GMLAN network during normal vehicle operation. Operating information
and commands are exchanged among the modules. Modules also learn and store the node
address's of the other modules on the GMLAN serial data bus. If a module fails to
detect a module that has been stored a DTC U2103 will set. Each module on GMLAN network
maintains a transmit error counter (TEC) and a receive error counter (REC). The counter
values increase with detected errors and will decrease with error-free messages. If
the TEC value exceeds 255 the controller removes itself from the network and a DTC
U2104 will be set.
Conditions for Running the DTCs
| • | Voltage supplied to the module is in the normal operating voltage range. |
| • | The vehicle power mode requires serial data communication to occur. |
Conditions for Setting the DTC
DTC U2103
The module does not detect a module on the GMLAN serial data bus that is stored
in memory.
DTC U2104
The module detects an error on the GMLAN serial data bus.
Action Taken When the DTCs Sets
| • | The module suspends all message transmission. |
| • | The module uses default values for all parameters received on the GMLAN
serial data circuits. |
| • | The module inhibits the setting of all other GMLAN communication DTCs. |
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
| • | DTC U2103 is likely an intermittent condition caused by a open on the
GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with CAN
Device procedure in order to isolate an intermittent condition. Refer to
Scan Tool Does Not Communicate with CAN Device
. |
