Scan Tool Does Not Communicate with Class 2 Device

Scan Tool Does Not Communicate with Class 2 Device

Circuit Description

Modules connected to the serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
3. A partial malfunction in the low speed GMLAN serial data circuit uses a different procedure from a total malfunction of the serial data circuit. The following modules communicate on the serial data circuit.

* Communication interface module (OnStar(R))
* Radio

5. DLC terminals 2 and 5 provide the connection to the serial data circuit and the signal ground circuit respectively.
7. A poor connection at splice pack S232 will cause this condition but will not set a DTC.
8. An open in the class 2 serial data circuit between the DLC and splice pack S232 will prevent the scan tool from communicating with any module on the class 2 network. This condition will not set a DTC.