| Table 1: | GMLAN ID |
Circuit Description
Modules connected to the high speed 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 prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, 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. GMLAN serial data messages contain 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 0xxx where xx is equal to the 3-digit identification number of the transmitter module.
The control module ID number list below provides a method for determining which module is not communicating. A module with a GMLAN serial data circuits 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 can not communicate.
Control Module | ID Number |
|---|---|
Engine Control Module (ECM) | 100 |
Transmission Control Module (TCM) | 101 |
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:
- Current DTCs before history DTCs unless told otherwise in the diagnostic table.
- The DTC which is reported the most times.
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. |
| • | The DTC U0001 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
The numbers below refer to the step numbers on the diagnostic table.
-
This DTC sets when a communication fault exists between the engine control module (ECM) and the TCM. Inspect for DTCs U0001 or U0101. If any of these DTCs are present, diagnose them first.
-
If a module is not awake, the modules expecting to receive data cannot detect the presence of the transmitting module.
-
The TCM needs time to reset memory.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems | |||||||||||
1 | Did you perform the Diagnostic System Check for the system exhibiting the symptom? | Go to Step 2 | Go to Control Module References in Body Control System for the applicable diagnostic system check | ||||||||
Test the following circuits of the TCM for an open or high resistance:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 6 | Go to Step 3 | |||||||||
3 | Test the CAN serial data low circuit and the CAN serial data high circuit between the engine control module (ECM) and TCM for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 6 | Go to Step 4 | ||||||||
4 | Inspect for poor connections at the harness connector of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 6 | Go to Step 5 | ||||||||
5 |
Important: Perform the set up procedure for the replaced control module if required. Replace the control module that is not communicating. Refer to Control Module References in Body Control System. Did you complete the replacement? | Go to Step 6 | -- | ||||||||
Does the DTC reset? | Go to Step 2 | System OK | |||||||||
