Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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 5-10 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. The following modules communicate on class 2 serial data circuit:
| Control Module | ID Number |
|---|---|
| Body Control Module (BCM) | 064 |
| Inflatable Restraint Sensing and Diagnostic Module (SDM) | 088 |
| Instrument Panel Cluster (IPC) | 096 |
| Head Up Display (HUD) | 098 |
| Radio | 128 |
| Digital Radio Receiver (DRR) | 137 |
| Communication Interface Module (OnStar®) | 151 |
| HVAC Control Module | 153 |
| Driver Door Module (DDM) | 160 |
| Passenger Door Module (PDM) | 161 |
| Driver Door Switch (DDS) | 164 |
| Driver Position Module (DPM) | 166 |
| Fold Top Controller (FTC) | 177 |
| Remote Control Door Lock Receiver (RCDLR) | 193 |
| Steering Column Lock Control Module (SCLCM) | 194 |
The BCM emulates some devices that are on high speed GMLAN serial data circuit to the modules on class 2 serial data circuit. The BCM transmits multiple Node Alive messages using source IDs that correspond to each of those high speed GMLAN nodes. This is in addition to the BCM behaving itself as a real node. The following module communicate on high speed GMLAN serial data circuit and are emulated by BCM on class 2 serial data circuit:
| Control Module | ID Number |
|---|---|
| Engine Control Module (ECM) | 017 |
| Transmission Control Module (TCM) | 024 |
| Electronic Brake Control Module (EBCM) | 040 |
When more than one Loss of Communication DTC is set in either one 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.
| DTC Symptom | DTC Symptom Descriptor |
|---|---|
| 00 | No additional information |
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.