Circuit/System Description
The control module runs a program to detect an internal fault when power up is commanded.
Some control modules must be configured with serial numbers, vehicle options, or other information. If a control module was not properly configured after installation, that module may set DTC B1001.
The internal fault detection is handled inside the control module.
The electrically erasable programmable read-only memory (EEPROM) check sum error detection is handled inside the control module.
When the ignition is turned ON, the microprocessor runs a diagnostic program to detect an internal fault when power up is commanded. If an internal malfunction is detected, the control module will store a DTC C0550 in its memory.
Modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
The body control module (BCM) activates the high speed GMLAN serial data wake up and the accessory wake up serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The high speed GMLAN serial data wake up circuit wakes up the electronic brake control module (EBCM) for bus communication and the accessory wake up serial data circuit wakes up the engine control module (ECM) and transmission control module (TCM).
The data link connector (DLC) is a standardized 16-cavity connector. Design and location is dictated by an industry-wide standard. The following is required to be provided
- Scan tool power battery positive voltage at terminal 16
- Scan tool power ground at terminal 4
- Common signal ground at terminal 5
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.
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The high speed GMLAN serial data circuits must be operational for the vehicle to start due to body control module (BCM) and engine control module (ECM) communications.
Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses SP 205 as the low speed splice pack or star connector.
Body Control System Description and Operation
The body control module (BCM) has a bussed electrical center integrated into the housing. Body control relays and fuses are installed directly on the BCM, which simplifies wiring and junction blocks on the vehicle. The body control system consists of the BCM and its associated controls. Battery positive voltage is provided to the BCM from IBCM BATT 1 fuse and the IBCM BATT 2 fuse in the underhood fuse block. The module grounds are wired to ground G201, G203 and G305. The BCM is wired to the GMLAN High speed serial data buss, and the GMLAN Low speed serial data buss, as well as discrete input and output terminals to control the functions of the vehicle's body.