2002 Chevy avalanche BCM Wiring Diagram

Chevrolet BODY CONTROL MODULE WIRING DIAGRAM

Ok, the bcm is a real possibility. the bcm is kinda a central computer for all the control m modules to communicate with each other. the engine control module, abs module, 4wd module, air bag module and dash are on what is called serial data circuit. kinda works like a network of computers. there is a circuit called data line that connects all these modules together, so each control module can talk to each other. if there is a problem with one of the modules or the line itself, it can cause all of these problems. we can rule the ecm out because it runs. this problem can be very hard to check out. you will have to start with checking all the power and grounds to each control module. if all this checks ok, then the data line system will have to be checked for any problems. if all the wiring check ok, then a bcm would be the likely problem. here is a wiring diagram on the data line.

The data link connector (DLC) allows a scan tool to communicate with 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; 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.