Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module's Node Alive message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx where xxx is equal to the 3-digit identification number is set.
The control module ID number list below provides a method for determining which module is not communicating. A module with a class 2 serial data circuit 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 |
|---|---|
Powertrain Control Module (PCM) | 016 |
Electronic Brake Control Module (EBCM) | 040 |
Body Control Module (BCM) | 064 |
Inflatable Restraint Sensing and Diagnostic Module (SDM) | 088 |
Instrument Panel Cluster (IPC) | 096 |
Vehicle Interface Unit (VIU) | 151 |
Instrument Panel Integration Module (IPM) | 152 |
Driver Door Module (DDM) | 160 |
Front Passenger Door Module (FPDM) | 161 |
Rear Passenger Door Module (RPDM) | 162 |
Memory Seat Module (MSM) | 166 |
Window Switch - Driver | 170 |
Remote Control Door Lock Receiver (RCDLR) | 176 |
Theft Deterrent Control Module | 192 |
When more than one Loss of Communication DTC is set in either 1 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.
- From the lowest number DTC to the highest number DTC.
Conditions for Running the DTC
| • | The following diagnostic trouble codes do not have a current status: |
| - | B1982 |
| - | B1983 |
| - | U1300 |
| - | U1301 |
| - | U1305 |
| • | The vehicle power mode requires serial data communication to occur. |
Conditions for Setting the DTC
A node alive message has not been received from a module with a learned identification number within the last 5 seconds.
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
When multiple Loss of Communication DTCs are set concurrently, the cause is likely to be 2 opens in the ring portion of the class 2 serial data circuit. Use the Control Module ID Number list in order to determine which modules are not communicating. Use the class 2 serial data circuit schematic in order to determine the location of the opens.
Test Description
The number below refers to the step number on the diagnostic table.
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 record any of the following DTCs?
| Go to Diagnostic Trouble Code (DTC) List in Doors | Go to Step 2 | ||||||||||||||||||||
2 |
Important: Use the control module ID number list in order to determine which modules are not communicating. Test the following circuits of the module that is not communicating for an open, short to ground or high resistance:
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 class 2 serial data circuits of the module that is not communicating for an open or high resistance. Refer to the following:
Did you find and correct the condition? | Go to Step 7 | Go to Step 5 | ||||||||||||||||||||
5 | Inspect the harness connector 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 7 | Go to Step 6 | ||||||||||||||||||||
6 |
Important: Perform the set up procedure for module if required. Replace the module that is not communicating. Refer to Control Module References for the applicable replacement procedure. Did you complete the replacement? | Go to Step 7 | -- | ||||||||||||||||||||
Does the scan tool display any DTCs which do not begin with a "U"? | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 8 | |||||||||||||||||||||
8 | 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 for the applicable Diagnostic System Check | Go to Step 9 | ||||||||||||||||||||
9 |
Did you complete the action? | Go to Control Module References for the applicable Diagnostic System Check | -- | ||||||||||||||||||||
