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 BCM
• The ECM
• 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 radio
• 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)
• The RDM