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. 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 U2100
will be set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC U2104 Controller Area Network (CAN) Bus Reset Counter Overrun
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
A certain number of no valid transmitted messages on the GMLAN serial data circuits
are detected by the module. The engine will not start when there is a total malfunction
of the high speed GMLAN serial data circuits while the engine is not running. The
following conditions may cause a total loss of high speed GMLAN data communication:
| • | A short between high speed GMLAN (+) and high speed GMLAN (-) circuits |
| • | Any of the high speed GMLAN serial data circuits shorted to ground or
voltage |
| • | A module internal malfunction that causes a short to voltage or ground
on the high speed GMLAN circuits |
| • | Any of the high speed GMLAN serial data circuits open |
Action Taken When the DTCs Sets
| • | The module suspends all message transmission. |
| • | The module uses default values for all parameters received on the high
speed GMLAN serial data circuits. |
| • | The module inhibits the setting of all other high speed 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
| • | An intermittent condition is likely to be caused by a short on the high
speed high speed GMLAN serial data circuits. Use the Scan Tool Does Not Communicate
with high speed GMLAN Device procedure in order to isolate an intermittent condition.
Refer to
Scan Tool Does Not Communicate with High Speed GMLAN Device
. |
