Data Link Connector: Description and Operation

DATA LINK COMMUNICATIONS DESCRIPTION AND OPERATION

CIRCUIT DESCRIPTION
The serial data communication among the control modules is performed through multiple serial data communication links. The class 2 serial data line is always present. The high speed GMLAN serial data lines are also present for the diesel option. The data link connector (DLC) allows a scan tool to communicate with the modules on class 2 or high speed GMLAN serial data lines. In order for the scan tool to communicate with the modules on high speed GMLAN link, a CANdi module is needed. The CANdi module behaves as an interface between the scan tool and the high speed GMLAN data link.

DATA LINK CONNECTOR (DLC)
The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following:
- Scan tool power battery positive voltage at terminal 16
- Scan tool power ground at terminal 4
- Common signal ground at terminal 5
- Class 2 signal at terminal 2
- High speed GMLAN serial data bus (+) at terminal 6
- High speed GMLAN serial data bus (-) at terminal 14

CLASS 2 SERIAL DATA LINE
Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. Class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7 volts during normal operation. Each module can pull this lower during the transmission. The bus is not at battery positive voltage or ground potential during normal operation. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a state of health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set a lost communication DTC associated with the loss of SOH for the non-communicating module. The DTC is unique to the module which is not communicating, for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.

The class 2 serial data line on this vehicle is a star configuration. The following modules communicate on the class 2 serial data line:
- The audible alert control module (CHIME) (w/UL5)
- The body control module (BCM)
- The electronic brake control module (EBCM)
- The inflatable restraint sensing and diagnostic module (SDM)
- The instrument panel cluster (IPC)
- The powertrain/engine control module (PCM/ECM)
- The radio
- The remote control door lock receiver (RCDLR)
- The engine control module (ECM) (Diesel)

The class 2 serial data line allows a scan tool to communicate with these modules for testing purposes, checking for DTCs, and to activate/enable/disable functions. These class 2 serial data circuits are bussed together at SP200-Refer to Master Electrical Component List for SP200 location.