Scan Tool Does Not Communicate with Low Speed GMLAN Device

Scan Tool Does Not Communicate with Low Speed GMLAN Device

Circuit 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. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

Test Description

Step 1 - Step 10:

The numbers below refer to the step numbers on the diagnostic table.
2. A current DTC U2100 71 or U2100 00 may be retrieved only from instrument panel module (IPM).
4. A partial malfunction in the low speed GMLAN serial data circuit uses a different procedure from a total malfunction of the low speed GMLAN serial data circuit. The scan tool communicates with the following modules on the low speed GMLAN serial data circuit:

* Audio amplifier
* Communication interface module (OnStar)
* Digital radio receiver (DRR)
* Driver door module (DDM)
* Driver door switch (DDS)
* Driver position module (DPM)
* Head up display (HUD)
* HVAC control module
* Inflatable restraint sensing and diagnostic module (SDM)
* Instrument panel cluster (IPC)
* Left rear door module (LRDM)
* Passenger door module (PDM)
* Radio
* Rear integration module (RIM)
* Remote control door lock receiver (RCDLR)
* Right rear door module (RRDM)
* Steering column lock control module (SCLCM)
* Television module

10. An open in the low speed GMLAN serial data circuit between the DLC and instrument panel module (IPM) will prevent the scan tool from communicating with any module on the low speed GMLAN bus. This condition will not set a DTC.