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 3 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 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 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 a hybrid ring and star 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. If there is one open on the star, the module not connected to the class 2 serial data circuit will not communicate. The following modules and splice packs are connected to the class 2 serial data circuit in a ring fashion:

The star has the following 3 splice packs:

The following devices are connected to the class 2 serial data circuit in star fashion via splice packs:

Refer to Data Link Connector Schematics in order to familiarize yourself with the architecture of the class 2 serial data circuit.

The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on 2 twisted wires that allow speed up to 500 Kbps. The twisted pair is terminated with two 120 ohm resistors, one is internal to the engine control module (ECM) and the other is internal to the transmission control module (TCM). The resistors are used to reduce noise on the high speed GMLAN bus during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level. The idle level which is approximately 2.5 volts is considered a recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes adds 1 volt to high speed GMLAN serial data bus (+) and subtracts 1 volt from high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0.

The modules on the GMLAN serial data line are:

The keyword protocols utilize a single wire bi-directional data line between the modules and the scan tool. The message structure is a request and response arrangement. The keyword serial data line is used for scan tool diagnostics only. The modules do not exchange data on this circuit.

The modules on the GMLAN serial data line are: