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 prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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 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

Circuit/System Testing

1. Test for less than 1.0 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 X4 harness connector at the BCM.
5. Verify a test lamp illuminates between ground circuit terminal E12 of the BCM and B+.

^ 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 and X4 harness connectors at the BCM.
11. Disconnect the appropriate harness connector at the ECM.

* RPO L61 - X1
* RPO LE5 - 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 TCM.
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 TCM and the ECM. If the circuits test normal, replace the TCM.

* RPO L61 - 43
* RPO L61 - 44
* RPO L61 - 43 and 44
* RPO LE5 - 33
* RPO LE5 - 53
* RPO LE5 - 33 and 53

15. Ignition OFF, disconnect the harness connector at the EBCM.
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 EBCM and the TCM. If the circuits test normal, replace the EBCM.

* 21
* 23

17. Ignition OFF, disconnect the X2 harness connector at the VCIM.
18. Attempt to communicate with the EPS. 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 TCM. If the circuits test normal, replace the VCIM.

* 9
* 8

19. Ignition OFF, disconnect the X2 harness connector at the BCM. Attempt to communicate with the EPS. 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 BCM and the VCIM. If the circuits test normal, replace the BCM.

* 2
* 20

20. Ignition OFF, disconnect the X2 harness connector at the EPS.
21. Ignition ON, test for less than 1 volt between the following serial data circuits of BCM and ground.

* 4
* 5

^ If greater than the specified range, test the circuit for a short to voltage.

22. Test for infinite resistance between the following serial data circuits of BCM and ground.

* 4
* 5

^ If less than the specified value, test the circuit for a short to ground.

23. Test for infinite resistance between the serial data circuits terminal 4 terminal 5 of the BCM.

^ If less than the specified Value, test the serial data circuits for a short between them.

24. If the circuits test normal, replace the EPS.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair. Verification Tests

* GMLAN Wiring Repairs