GMLAN Low Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a single wire to the appropriate control modules. Under normal vehicle operating conditions, the speed of the buss is 33.33 Kb/s. This protocol produces a simple pulse train sent out over the GMLAN low speed serial data bus. When a module pulls the buss high, 5 volts, this creates a logic state of 0 on the buss. When the buss is pulled low, 0 volts, it is translated as a logic state of 1. To wake the control modules connected to the GMLAN low speed serial data buss, a high voltage wake up pulse is sent out over the buss, the voltage level of the pulse is +10 volts. Modules connected to the GMLAN low speed buss can be part of a virtual network as described in GMLAN High Speed Circuit Description above. The modules on the GMLAN low speed serial data buss are connected to the buss using several splice or "star" connectors separating groups of modules. Refer to Data Communication Schematics  for specific schematics information.

The following lists state the splices and modules connected to the low speed serial data circuits:

I/P Splice

• BCM
• Secondary information centre (SIC)
• Instrument panel cluster (IPC)
• Inflatable Restraint Sensing and Diagnostic Module (SDM)
• Theft deterrent module (TDM)
• Infotainment unit - integrated radio chassis (IRC)
• Heating ventilation and cooling (HVAC) control module
• Remote function actuator (RFA)
• Active occupant sensing (AOS) module
• Heated seat module
• OnStar® vehicle communication interface module (VCIM)