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 7.0 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.
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. |
Class 2 Serial Data Line
The class 2 serial data communications circuit on this vehicle is in
a star configuration. This configuration has a splice pack, located nearby the DLC.
The following modules communicate on the class 2 serial data circuit:
| • | 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 control module (PCM) |
| • | The remote control door lock receiver (RCDLR) |
| • | The vehicle communication interface module (VCIM) |
