VUE AWD V6-3.5L (2007)
Information Bus: Description and Operation
Data Link Communications Description and Operation
Circuit Description
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 serial data at terminal 2
* Keyword serial data at terminal 7
* Keyword serial data at terminal 12
* Low Speed GMLAN serial data at terminal 1, with U32 or U2K
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 4 different
types of protocols on this vehicle.
* The class 2 serial data
* The control area network (CAN) serial data
* The low speed GMLAN serial data
* The Keyword 2000
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.
Class 2 Serial Data Circuit
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 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.
The class 2 serial data circuit on this vehicle consists of ring 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. The only exception from the ring configuration is the communication interface module (OnStar), with
UE1, that is connected to splice S203. The following modules are connected to the class 2 serial data circuit in a ring fashion
* Body control module (BCM)
* Instrument panel cluster (IPC)
* Power steering control module (PSCM)
* The inflatable restraint sensing and diagnostic module (SDM)
CAN Serial Data Circuit
The controller area network (CAN) serial data line is used for functional messages only and does not communicate with the scan tool via the data link
connector (DLC). The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most
important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is
assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission
attempt as soon as the bus is free again.
The body control module (BCM) acts as gateway between CAN and class 2 serial data lines, transmitting messages from one subnet to another. The
BCM emulates the CAN modules on the class 2, embedding the original transmitter ID in translated CAN messages to class 2. Therefore the class 2
modules can set specific non communications DTCs against CAN modules. This concept doesn't apply for class 2 to CAN transmitted messages.
Therefore the CAN modules consider the BCM as being the originator of all class 2 messages that they receive. The following modules communicate on
