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. Use the Control Module ID Number list in order to determine which module is not communicating and the Lost Communications with 1XXX diagnostic table in order to diagnose the malfunction.
Control Module | ID Number |
|---|---|
Electronic Brake Control Module (EBCM) w/EBC 310 | 041 |
Electronic Brake Control Module (EBCM) w/EBC 325 | 042 |
Powertrain Control Module (PCM)/Vehicle Control Module (VCM) | 016 |
Vehicle Immobilizer Module (VIM) | 193 |
Vehicle Theft Deterrent Passlock Module (VTD) | 192 |
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 (Node Alive messages). 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 two seconds. When no message is detected from a learned identification number for five seconds, a DTC U1xxx (where xxx is equal to the three digit identification number) is set.
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating voltage range (approximately 9 - 16 volts). |
| • | The vehicle power mode (ignition switch position) requires serial data communication to occur. |
Conditions for Setting the DTC
A message from a learned identification number has not been detected for the past five seconds.
Conditions for Clearing the DTC
| • | A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle. |
| • | A history DTC will clear upon receipt of a scan tool Clear DTCs command. |
Diagnostic Aids
| • | An intermittent open, short to ground, or short to B+ between the inoperative module and the data line may cause this code to set. |
| • | A poor connection at the inoperative module or the data line may cause this code to set. |
| • | An intermittent open in the data line may cause this code to set. |
Test Description
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A module which loses power during an ignition cycle will cause other module(s) to set Lost Communication DTCs.
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The malfunction may be due to an open in the class 2 serial data circuit or an open in the module circuit.
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The module which was not communicating due to an open in the class 2 serial data circuit and may have set Lost Communication DTCs for those modules that it was monitoring.
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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 |
|---|---|---|---|
Perform the Diagnostic System Check for the module which does not communicate to ensure that the module is properly powered. Was a repair made when the Diagnostic System Check was performed? | |||
Test the class 2 serial data circuit of the module that is not communicating for an open between itself and the module reporting the U-code. Refer to Wiring Repairs . Did you find and correct the condition? | |||
3 | Inspect for poor connections/terminal tension at the class 2 serial data circuit(s) of the module that is not communicating. Refer to Connector Repairs . Did you find and correct the condition? | ||
4 | Replace the module that is not communicating. Refer to the appropriate repair instructions for module replacement. Did you complete the replacement? | -- | |
5 |
Does the scan tool display any DTCs which do not begin with a U? | Go to the applicable DTC table | |
Clear the DTCs using the scan tool. Did you complete the action? | -- | ||
7 | Select the display DTCs function for the module(s) which had the Lost Communications with XXX DTC set. Does the scan tool display any DTCs which do not begin with a U? | Go to the applicable DTC table | |
Did you complete the action? | System OK | -- |
