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 is set.
The Control Module ID Number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a Lost Communication DTC set by other modules. The modules that can communicate will set a DTC indicating the module that cannot communicate. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx is set.
Control Module | ID Number |
|---|---|
PCM | 016 |
Transfer Case Shift Control Module | 026 |
EBCM | 041 |
BCM | 064 |
SDM | 088 |
IPC | 096 |
HVAC Control Module | 152 |
MSM | 166 |
VTD | 192 |
When more than one Loss of Communication DTC is set in either one module of in several modules, diagnose the DTCs in the following order:
- Current DTCs before history DTCs unless told otherwise in the diagnostic tables.
- The DTC which is reported the most times.
- From the lowest number DTC to the highest number DTC.
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating voltage range of 9-16 volts. |
| • | DTCs U1300, U1301 or U1305 do not have a current status. |
| • | The vehicle power mode requires serial data communication to occur. |
Conditions for Setting the DTC
A message containing a critical operating parameter has not been received within the last 5 seconds after establishing class 2 serial data communication.
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
| • | An intermittent open between a module and a star connector may cause this DTC to set. |
| • | A poor connection at a module or a star connector may cause this DTC to set. |
| • | An intermittent open in a star connector may cause this DTC to set. |
| • | An open voltage or ground circuit to a module may cause this DTC to set. |
| • | An internal module malfunction may cause this DTC to set. |
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 |
Important: Use the control module ID number list in order 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 6 | Go to Step 2 | ||||||||||||||||||||
2 |
Refer to the following:
Did you find and correct the condition? | Go to Step 6 | Go to Step 3 | ||||||||||||||||||||
3 | Test the class 2 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 6 | Go to Step 4 | ||||||||||||||||||||
4 | 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 6 | Go to Step 5 | ||||||||||||||||||||
5 |
Important: Perform the programming or set up procedure for the 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 6 | -- | ||||||||||||||||||||
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 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 for the applicable Diagnostic System Check | Go to Step 8 | ||||||||||||||||||||
8 |
Did you complete the action? | Go to Control Module References for the applicable Diagnostic System Check | -- | ||||||||||||||||||||
