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 |
• | High speed GMLAN serial data bus (+) at terminal 6 |
• | High speed GMLAN serial data bus (-) at terminal 14 |
Class 2 Circuit Description
The data link connector (DLC) allows a scan tool to communicate with the class 2
serial data circuit. Class 2 serial data is transmitted on a single wire at
an average of 10.4 Kbps. The bus is active at 7 volts nominal and inactive
at ground potential. 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 body control module (BCM) SOH message disappears, several modules set DTC U1064.
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 line on this vehicle is a star configuration.
There are 2 additional class 2 serial data circuits from the BCM to
the engine control module (ECM) and to the transmission control module (TCM), w/M32.
The following modules are attached to splice pack SP201:
• | The auxiliary gage center, w/ERG or ERH |
• | The electronic brake control module (EBCM) |
• | The inflatable restraint sensing and diagnostic module (SDM) |
• | The instrument panel cluster (IPC) |
• | The memory seat module (MSM) - driver, w/AAB |
• | The rear/door module (RDM), w/base audio |
• | The remote control door lock receiver (RCDLR) |
For premium audio option, the following modules are attached to splice pack SP300:
• | The audio amplifier (AMP) |
GMLAN Circuit Description
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 signal supervision is the process of
determining whether an expected signal is being received or not. Failsofting is the
ability to substitute a signal with a default value or a default algorithm, in the
absence of a valid signal. Some messages are also interpreted as a "heartbeat"
of a virtual device. If such a signal is lost, the application will set a no communication
code against the respective virtual device. Note that a loss of serial data DTC does
not normally represent a failure of the module that set it.
The following modules are connected to the high speed GMLAN serial data communication
circuits: