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. Each message contains the identification number of the transmitter module.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC U0100 Lost Communication With Engine Control Module (ECM) |
| • | DTC U0101 Lost Communication With Transmission Control Module (TCM) |
| • | DTC U0140 Lost Communication With Body Control Module (BCM) |
| • | DTC U0121 Lost Communication With Antilock Brake Module (ABS) |
Conditions for Running the DTC
| • | 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. |
Step | Action | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List | |||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |||||||||||||||||
2 | Did you record DTC U0001, U0073 or U1000? | Go to Step 3 | |||||||||||||||||
3 |
Important: Use the DTC list in DTC Descriptors to determine which module is not communicating. Test the following circuits of the module that is not communicating for an open or a short to ground:
Refer to the following:
Did you find and correct the condition? | Go to Step 8 | Go to Step 4 | ||||||||||||||||
4 |
Refer to the following:
Did you find and correct the condition? | Go to Step 8 | Go to Step 5 | ||||||||||||||||
5 | Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and GMLAN Wiring Repairs . Did you find and correct the condition? | Go to Step 8 | Go to Step 6 | ||||||||||||||||
6 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits:
Refer to the following:
Did you find and correct the condition? | Go to Step 8 | Go to Step 7 | ||||||||||||||||
7 | Replace the module that is not communicating. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 8 | -- | ||||||||||||||||
8 | Use the scan tool in order to clear the DTCs. Does the scan tool still display other current DTCs? | -- | |||||||||||||||||
