Circuit Description
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. If any of the CAN circuits are shorted to battery voltage, ground, or between them no communication is possible on the CAN serial data bus, a DTC U2104 is set.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC U1800 Lost Communications With Fuel Injector Control Module (FICM) |
| • | DTC U2105 Lost Communications With Engine Control Module (ECM) |
| • | DTC U2106 Lost Communications With Transmission Control Module (TCM) |
Conditions for Running the DTCs
| • | Voltage supplied to the modules is in the normal operating voltage range. |
| • | The engine is running. |
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. |
| • | The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and fails, for the type B DTCs. For a detailed description about DTC types, refer to Diagnostic Trouble Code (DTC) Type Definitions in Engine Controls - 6.6L (LB7). |
Conditions for Clearing the MIL/DTC
The MIL/DTC clearing depends on DTC type. For information about DTC types, refer to Diagnostic Trouble Code (DTC) Types in Engine Controls - 6.6L (LB7).
DTC Type B
| • | The MIL clears after three ignition cycles when the malfunction is no longer present. |
| • | 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. |
DTC Type C
| • | 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.
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A total loss of communication on the CAN serial data link should be diagnosed first.
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The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
Step | Action | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||||||||||||||||||||||
Is DTC U2104 set as current? | Go to DTC U2104 | Go to Step 2 | |||||||||||||||||||||
2 |
Important: Use the control module ID number list in order to determine which module is not communicating on the controller area network (CAN) serial data bus.
Refer to the following procedures:
Did you find and correct the condition? | Go to Step 7 | Go to Step 3 | ||||||||||||||||||||
3 |
Refer to the following procedures:
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 on the CAN serial data bus 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 the CAN serial data bus for poor connections and terminal tension at the following circuits:
Refer to the following procedures:
Did you find and correct the condition? | Go to Step 7 | Go to Step 6 | ||||||||||||||||||||
6 |
Important: Perform the programming or set up procedure for the module, if required. Replace the module that is not communicating on the CAN serial data bus. Refer to Control Module References for the applicable replacement procedure. Did you complete the replacement? | Go to Step 7 | -- | ||||||||||||||||||||
7 | Select the Display DTCs function for the modules which had the Loss of Communications DTC set. Does the scan tool display any DTCs which do not begin with a "U"? | Go to Control Module References in Body Control System | Go to Step 8 | ||||||||||||||||||||
Did you complete the action? | Go to Control Module References in Body Control System | -- | |||||||||||||||||||||
