Scan Tool Does Not Communicate with High Speed GMLAN Device
Scan Tool Does Not Communicate with High 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 body control module (BCM) and engine control module (ECM) communications.
Diagnostic Aids
* Communication may be available between the BCM 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 (Initial Inspection and Diagnostic Overview) to identify the high speed GMLAN serial data modules.
* This test is used for a total high speed GMLAN communication failure. If only one module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
* An open in the DLC ground circuit terminal 5 will allow the scan tool to operate and 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)
* Control Module References (Programming and Relearning)
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
1. Test for less than 1 ohm between the ground circuit terminal 5 of the DLC and ground.
• If greater than the specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the X2 harness connector at the BCM.
3. Test for less than 2 ohms on the serial data circuit between terminal 6 of the DLC and terminal 1 of the BCM.
• If greater than the specified range, test the serial data circuit for open/high resistance.
4. Ignition OFF, disconnect the X3 and X4 harness connector at the BCM.
5. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
* X2 terminal 13
* X3 terminal 12
* X4 terminal E12
• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
6. Ignition ON, verify a test lamp illuminates between each B+ circuit terminal D12 of the BCM and ground.
• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground.
7. Ignition ON, test for less than 1 volt between the serial data circuit terminal 6 of the DLC and ground, and terminal 14 of the DLC and ground.
• If greater than the specified range, test the serial data circuit for a short to voltage.
8. Test for infinite resistance between the serial data circuit terminal 6 of the DLC and ground, and terminal 14 of the DLC and ground.
• If less than the specified value, test the serial data circuit for a short to ground.
9. Test for infinite resistance between the serial data circuits terminal 6 and terminal 14 of the DLC.
• If less than the specified value, test the serial data circuits for a short between them.
10. Connect the X2, X3, and X4 harness connectors at the BCM.
11. Disconnect the appropriate harness connector at the ECM.
* RPO LZ4 - X1
* RPO LY7 - X3
* RPO HP7 - X3
12. Attempt to communicate with the vehicle control interface module (VCIM). Communication should not be available.
• If communication is available, replace the ECM.
13. Ignition OFF, disconnect the harness connector at the SGCM (RPO - HP7).
14. Attempt to communicate with the VCIM. Communication should not be available.
• If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the SGCM and the ECM. If the circuits test normal, replace the TCM.
* Terminal 11
* Terminal 23
15. Ignition OFF, disconnect the harness connector at the TCM.
16. Attempt to communicate with the VCIM. Communication should not be available.
• If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCM and the SGCM. If the circuits test normal, replace the TCM.
* RPO MH2 - 12
* RPO MH2 - 5
* RPO MH2 - 5 and 12
* RPO MN5 - 37
* RPO MN5 - 38
* RPO MN5 - 37 and 38
17. Ignition OFF, disconnect the harness connector at the EBCM.
18. Attempt to communicate with the VCIM. Communication should not be available.
• If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM and the TCM. If the circuits test normal, replace the EBCM.
* B12
* B9
19. Ignition OFF, disconnect the X2 harness connector at the power steering control module.
20. Attempt to communicate with the VCIM. Communication should not be available.
• If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the suspension control module and the terminator resistor. If the circuits test normal, replace the power steering control module.
* 1
* 2
21. Ignition OFF, disconnect the X3 harness connector at the VCIM. Attempt to communicate with the BCM. Communication should not be available.
• If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the VCIM and the suspension control module. If the circuits test normal, replace the VCIM.
* 9
* 8
22. Ignition OFF, disconnect the X2 harness connector at the BCM.
23. Ignition ON, test for less than 1 volt between the following serial data circuits of BCM and ground.
* 20
* 2
• If greater than the specified range, test the circuit for a short to voltage.
24. Test for infinite resistance between the following serial data circuits of BCM and ground.
* 20
* 2
• If less than the specified value, test the circuit for a short to ground.
25. Test for infinite resistance between the serial data circuits terminal 20 terminal 2 of the BCM.
• If less than the specified value, test the serial data circuits for a short between them.
26. If the circuits test normal, replace the BCM.
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)