| Table 1: | The Control Module ID |
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 (ID) 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 ID number is learned by a module, it will monitor for that modules node alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. When no message is detected from a learned ID number for 5 seconds, a DTC U1XXX. XXX is equal to the 3 digit ID number of the module.
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 XXX diagnostic table in order to diagnose the malfunction. When no message is detected from a learned ID number for 5 seconds, a DTC U1XXX is set.
Control Module | ID Number |
|---|---|
Powertrain/Engine Control Module (PCM/ECM) | 016 |
Regulated Voltage Controller (RVC) | 022 |
Hybrid Control Module (HCM) | 023 |
Transmission Control Module (TCM) | 024 |
Transfer Case Shift Control Module (TCSCM) | 026 |
Electronic Brake Control Module (EBCM) | 041 |
Rear Wheel Steering Control Module (RWSCM) | 048 |
Body Control Module (BCM) | 064 |
Inflatable Restraint Sensing and Diagnostic Module (SDM) | 088 |
Instrument Panel Cluster (IPC) | 096 |
Driver Information Center (DIC) | 097 |
Radio | 128 |
Audio Amplifier (AMP) | 129 |
Remote Playback Device - CD Player (CDX) | 130 |
Digital Radio Receiver (DRR) | 137 |
Communication Interface Module (OnStar®) | 151 |
HVAC Control Module | 152 |
Rear Seat Entertainment (RSE) Assembly | 154 |
Driver Door Module (DDM) | 160 |
Passenger Door Module (PDM) | 161 |
Memory Seat Module (MSM) | 166 |
Rear Seat Audio Controller (RSA) | 167 |
When more than one loss of communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order:
- Current DTCs before history DTCs except as specified 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 node alive message has not been received from an identified module 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
| • | 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.
-
The module which was not communicating on the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.
Step | Action | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Communication Schematics Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views | |||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |||||||||||||||||
2 |
Important: Use the control module identification (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 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. Refer to Circuit Testing and Wiring Repairs . 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 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. Refer to Control Module References for replacement, setup, and programming. 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 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 Step 9 | |||||||||||||||||
9 |
Did you complete the action? | System OK | -- | ||||||||||||||||
