Theory Of Operation

Below are a few different ways communication on a vehicle takes place:

1. Scan tool to the Gateway Module
2. Module to Module
3. Module to Device
4. Device to Module

Communication to the vehicle is established with a scan tool, through the Data Link Connector (DLC) to a Gateway Module over the Controller Area Network (CAN) Bus. On this vehicle the Security Gateway (SGW) Module communicates with the scan tool through the CAN-C and CAN-IHS Bus networks.

The CAN Bus architecture of this vehicle operates in a "hub" or "star" style, meaning all of the modules are connected at a central point in the Star Connectors. The terminating resistors for CAN Bus are located in the Star Connectors and are a part of the body and instrument panel wiring harnesses.

In other CAN Bus architectures a vehicle may operate in a "stub" or "backbone" style, meaning there is a single, main line that connects all modules. The terminating resistors for a CAN Bus in the "stub" or "backbone" style are located in 2 separate dominant modules and are placed as far apart in the vehicle, as is physically possible.

The header of the scan tool is populated by the BCM with vehicle data, when communication with the scan tool has been established through the SGW Module. The scan tool becomes another module on the vehicle's networks by acting as the Master Module of all Bus networks while connected to the DLC, and contributes voltage to the operation of the CAN Bus.