Scan Tool Does Not Communicate with Mid Speed GMLAN Device
Scan Tool Does Not Communicate with Mid 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 high speed GMLAN serial data circuits 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 high speed GMLAN serial data circuits must be operational for the vehicle to start due to steering column control module (SCCM) and engine control module (ECM) communications. The vehicle theft deterrent (VTD) module and ECM exchange information using the BCM as the gateway module allowing communication between the high and low speed serial data buses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial data bus uses two 120-ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is in the rear cargo area and the other is internal to the ECM.
Diagnostic Aids
* Communication may be available between the SCCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the high and low speed GMLAN systems.
* Use the Data Link References (Data Link References) to identify the high speed GMLAN serial data modules.
* This test is used for a total high speed GMLAN communication malfunction. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
* Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module.
* An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module detected" and will not communicate.
* The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus. The following conditions may cause a total loss of high speed GMLAN data communication:
- A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
- Any of the high speed GMLAN serial data circuits shorted to ground or voltage
- A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
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 Verification
Attempt to communicate with all modules on the mid speed GMLAN bus.
If any high speed module communicates and any DTC beginning with a U exists, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions) .
If any high speed module communicates and no DTC beginning with a U exists, refer to DTC U2105-U2199 (U2106) .
Circuit/System Testing
1. Ignition OFF, test for less than 1.0 ohm between the data link connector (DLC) ground circuit terminal 5 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
2. Ignition OFF, disconnect the X1 harness connector at the infotainment display.
3. Ignition OFF, test for less than 2 ohms between the DLC serial data circuit terminal 3 and CIM serial data circuit terminal 22.
• If greater than the specified range, test the serial data circuit for open/high resistance.
4. Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
* Terminal 3
* Terminal 11
• If less than the specified value, test the serial data circuits for a short to ground.
5. Ignition ON, test for less than 1-volt between the following serial data circuits of the DLC and ground.
* Terminal 3
* Terminal 11
• If greater than the specified range, test the serial data circuit for a short to voltage.
6. Ignition OFF, test for infinite resistance between the DLC serial data circuit terminal 3 and terminal 11.
• If less than the specified value, test for a short between the serial data circuits.
7. Connect the X1 harness connector at the infotainment display.
8. Ignition OFF, disconnect the X1 harness connector of the radio.
9. Ignition ON, attempt to communicate with the display unit. Communication should not be available.
• If communication is established, replace the radio.
10. Ignition OFF, disconnect the X1 harness connector of the infotainment display.
11. Ignition OFF, test for infinite resistance between the following serial data circuits and ground.
* Terminal 19
* Terminal 20
• If less than the specified value, test the serial data circuit for a short to ground.
12. Ignition ON, test for less than 1-volt between the following serial data circuits and ground.
* Terminal 19
* Terminal 20
• If greater than the specified range, test the serial data circuit for a short to voltage.
13. Ignition OFF, test for infinite resistance between the serial data circuit terminal 19 and terminal 20.
• If less than the specified value, test for a short between the serial data circuits.
14. If the circuits test normal, replace the infotainment display.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
Control Module References (Programming and Relearning)for control module replacement, setup, and programming
GMLAN Wiring Repairs (Component Tests and General Diagnostics)