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:

The serial data circuits are the means by which the control modules on the vehicle communicate with each other and the scan tool. There are 4 different types of protocols on this vehicle.

The scan tool will power up with the ignition off. Some modules however, will not communicate unless the ignition is on and the power mode master (PMM) module sends the appropriate power mode message. Refer to Body Control System Description and Operation for operation of the PMM.

The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data line. This serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Once the scan tool is connected to the class 2 serial data line through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average, 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 7.0 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 an internal DTC associated with the loss of SOH of 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 circuit on this vehicle consists of ring configuration. Each module on the ring has 2 class 2 serial data circuits connected to it. If there is one open on the ring serial data communication will still take place. If there is more than one open on the ring, the modules not connected to the class 2 serial data circuit will not communicate. The only exception from the ring configuration is the communication interface module (OnStar), with UE1, that is connected to splice S203. The following modules are connected to the class 2 serial data circuit in a ring fashion

The controller area network (CAN) serial data line is used for functional messages only and does not communicate with the scan tool via the data link connector (DLC). The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.

The body control module (BCM) acts as gateway between CAN and class 2 serial data lines, transmitting messages from one subnet to another. The BCM emulates the CAN modules on the class 2, embedding the original transmitter ID in translated CAN messages to class 2. Therefore the class 2 modules can set specific non communications DTCs against CAN modules. This concept doesn't apply for class 2 to CAN transmitted messages. Therefore the CAN modules consider the BCM as being the originator of all class 2 messages that they receive. The following modules communicate on the CAN serial data line:

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. The transmission speed for low speed GMLAN is up to 83.33 Kbps. This high speed is used for programming purposes only. Under normal vehicle operating conditions the speed of the bus is 33.33 Kbps. This protocol produces a simple pulse train sent out over the low speed GMLAN serial data bus. To wake up the control modules connected to the low speed GMLAN serial data bus, a wake-up pulse of 10 volts is sent out over the bus.

The modules on the low speed GMLAN serial data line are:

The Keyword protocols utilizes a single wire bi-directional data line between the modules and the scan tool. The message structure is a request and response arrangement. Keyword 2000 is used for scan tool diagnostics only. The modules do not exchange data on these systems. They are two independent Keyword serial data circuits connected to data link connector (DLC) terminals 7 and 12. The following modules communicate with scan tool through Keyword 2000 serial data circuits:

Keyword serial data to DLC terminal 7

Keyword serial data to DLC terminal 12

Electronic brake control module (EBCM)