Circuit Description
Important: For DTC U0107 refer to DTC U0107 in Engine Controls - 3.5L (L66)
Modules connected to the controller area network (CAN) 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. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module. A module with a CAN 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.
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 U0121 Lost Communication With Electronic Brake Control Module (EBCM) |
| • | DTC U0140 Lost Communication With Body Control Module (BCM) |
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 U0073 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
Important: The scan tool communicates with the BCM on class 2 bus and with electronic brake control module (EBCM) on Keyword 2000 bus. The above DTCs are set for communication on CAN bus. For example, if DTC U0121 is set, the scan tool may communicate properly with the EBCM, but EBCM may not functionally communicate properly on CAN bus. Refer to Data Link Communications Description and Operation .
| • | 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 in Wiring Systems | |||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||||||||||||
2 |
Important: Use the DTC list in DTC Descriptors to determine which is the module that is not communicating on controller area network (CAN) bus. Test the following circuits of the module that is not communicating on CAN bus for an open or a short to ground:
Refer to the following:
Did you find and correct the condition? | Go to Step 7 | Go to Step 3 | ||||||||||||||||||||
3 |
Refer to the following:
Did you find and correct the condition? | Go to Step 7 | Go to Step 4 | ||||||||||||||||||||
4 | Test the CAN serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 7 | Go to Step 5 | ||||||||||||||||||||
5 | Inspect the harness connectors of the module that is not communicating on CAN bus for poor connections and terminal tension at the following circuits:
Refer to the following:
Did you find and correct the condition? | Go to Step 7 | Go to Step 6 | ||||||||||||||||||||
6 | Replace the module that is not communicating on CAN bus. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 7 | -- | ||||||||||||||||||||
7 | Use the scan tool in order to clear the DTCs. Does the scan tool still display other current DTCs? | Go to the Diagnostic System Check - Vehicle in Vehicle DTC Information | -- | ||||||||||||||||||||
