Circuit Description
The data link connector (DLC) allows a scan tool to communicate with modules
on 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 and 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
located below the instrument panel and close to the steering column. Connector design
and location is dictated by an industry wide standard, and it 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 serial data signal at terminal 2 |
Class 2 Serial Data Line
The class 2 serial data line on this vehicle is a star configuration.
The following modules are attached to SP 261 and communicate on the class 2
serial data line:
| • | The body control module (BCM) |
| • | The driver information center (DIC) |
| • | 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 transfer case shift control module (TCCM) |
