Scan Tool Does Not Communicate with Low Speed GMLAN Device
Scan Tool Does Not Communicate with Low Speed GMLAN Device
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and Steering Colum Control Module (SCCM) can communicate.
Diagnostic Aids
* Use the Data Link References (Data Link References) to identify the low speed GMLAN serial data modules.
* An open in the low speed GMLAN serial data circuit between the first module from the DLC and a module(s) will only effect the specific module(s). This type of failure will set a loss of communication DTC for each module effected, and the other modules will still communicate. Depending on which module is effected, the vehicle may not start.
* An open between the data link connector (DLC) and the first module will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start.
* Use the DMM MIN/MAX function to capture/locate intermittent conditions.
* The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit.
The following conditions may cause a total loss of low speed GMLAN data communication:
- The low speed GMLAN serial data circuit shorted to ground or voltage.
- A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit.
Reference Information
Schematic Reference
Data Communication Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Data Link Communications Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information.
Circuit/System Testing
LS GMLAN initial test
1. Ignition OFF, disconnect the X1 harness connector at the CIM.
2. Ignition ON, test for less than 1.0 volt between the low speed GMLAN serial data circuit of the DLC and ground.
• If greater than the specified range, test the serial data circuit for a short to voltage.
3. Test for infinite resistance between the serial data circuit of the DLC and ground.
• If less than infinite resistance, test the serial data circuit for a short to ground.
4. Test for less than 1.0 ohm of resistance in the serial data circuit between the DLC and the CIM.
• If greater than the specified range, test the serial data circuit for an open/high resistance.
5. Disconnect the X1 harness connector at the SDM, install a 3-amp fused jumper wire from the SDM terminal 35 to the harness side of X1.
6. With a scan tool, attempt to communicate with the IPC.
• If communication is established, refer to Diagnostic 2
• If communication is not established, refer to Diagnostic 1
LS GMLAN test 1
1. Remove the jumper wire from the SDM.
2. Disconnect the folowing harness connectors for the following modules.
* REC X5
* UEC X2
* IPC X1
* SCCM X1
3. Test each serial data circuit of the disconnected modules for a short to voltage or a short to ground, with the modules disconnected. If the circuit tests normal, install each module one at a time in the following order, while attempting to commuinicate after each module is connected until communications stop.
* SCCM X1
* IPC X1
* UEC X2
* REC X5
4. Replace the last module connected that caused communication to stop.
LS GMLAN test 2
1. Remove the jumper wire from the SDM.
2. Install a 3 amp fused jumper wire between termial 37 and 38 on the harness side of the SDM X1 harness connector.
3. Attempt to commuinicate with the AHS, communication should not be available.
• If communication is establihed, replace the SDM.
4. Disconnect the jumper wire for the harness side of the SDM X1 harness connector.
5. Disconnect the folowing harness connectors of the following modules.
* Auxiliary HVAC Module X1
* TPM X1
* Infotainment display unit X1
* SCCM X1
6. Test each serial data circuit of the disconnected modules for a short to voltage or a short to ground, with the modules disconnected. If the circuit tests normal, install each module one at a time in the following order, while attempting to commuinicate after each module is connected until communications stop.
* SCCM X1
* Infotainment display unit X1
* SDM X1
* TPM X1
* Auxiliary HVAC Module X1
7. Replace the last module connected that caused communication to stop.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Control Module References (Programming and Relearning) for module replacement, setup, and programming
* GMLAN Wiring Repairs (Component Tests and General Diagnostics)