For 1990-2009 cars

### Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data line. The 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 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.

### 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

• | Class 2 serial data at terminal 2

• | Common signal ground at terminal 5

### Class 2 Serial Data Line

The class 2 serial data line on this vehicle is a combination ring-star configuration, where body control module (BCM) is connected to multiple modules. Refer to Data Communication Schematics . The following modules communicate on class 2 bus:

• | The BCM

• | The communication interface module (OnStar®), w/UE1

• | The digital radio receiver (DRR), w/U2K

• | The electronic brake control module (EBCM)

• | The inflatable restraint sensing and diagnostic module (SDM)

• | The instrument panel cluster (IPC)

• | The powertrain control module (PCM)

• | The radio

• | The transfer case shift control module (TCSCM), w/4WD