Corvette V8-5.7L VIN G (1997)
Some electrical components are directly connected and controlled by their system module. Others systems accomplish this by sharing data information
with other systems on the serial data line to execute various vehicle functions. All system data information (sensors, switches, etc.) can be monitored by
any system module that completes the computer system. All systems on the same serial data line use a communication process similar to a telephone
system, where enormous amounts of information can be exchanged on a single data wire.
Communications between each system is accomplished by sending a digitally coded message, consisting of specific information a system module must
follow. Each system module is assigned its own recognition code (address). So when a message is sent out on the serial data line, only the particular
system module that was assigned that recognition code will responded to the message.
The Body Control Module (BCM), which is the power mode master, is responsible for sending a power mode message on the serial data line to other
systems. When the power mode message is sent, other systems respond to this message by entering a power-up state and sending a State of Health Code
(SOH) code message. This SOH message indicates they are able to communicate information between other systems.
By communicating data information with other systems on the same serial data line, either input information or specific program information within the
systems memory, can provide more accurate and reliable computer system control functions. The BCM uses information from other systems in order to
execute some functions. Therefore, before further diagnosis, review the general information on how the BCM computer system operates and how each
system interacts with the BCM. This will save diagnostic time, future misdiagnosis, and unnecessary parts replacement.
Interior Lamp Over Voltage Protection
The Body Control Module (BCM) disables the interior lamp bulbs when the system voltage is above 18.0 volts in order to extend the bulb life.
Load Shed Control
The Body Control Module (BCM) can turn off the rear window defogger and heated outside mirror electrical loads when the vehicle is in a condition
where these loads may discharge the battery. The BCM will also remove these loads when engine demands are higher.
Monitored Loads
In order to minimize any battery rundown, the Body Control Module (BCM) can detect if certain electrical loads have been left on. When the BCM
detects that the ignition has been cycled to the OFF position, the BCM immediately checks the status of the load monitor input. If the BCM detects that a
load is present (ground on CKT 640), the BCM turns ON the load monitor relay for 15 minutes. If after 15 minutes the BCM still recognizes that a load
is present, the BCM will turn OFF the relay, removing the battery voltage from the loads. The BCM continues to monitor this circuit for a switch
transition. The BCM will again turn ON the relay for 15 minutes if a switch transition exists.
Power Requirements
The Body Control Module (BCM) has two main power feeds (high and low current), and two main grounds. The low power feed (battery 1) is used to
provide power for the BCM's logic and internal driver operation. The high power feed (battery 2) is used to provide power for systems that draw higher
amounts of current (motors, lights, etc.). Operating current at the BCM's battery should not exceed 3.0 amperes at battery 1, and 7.5 amperes (for 2
seconds) at battery 2 while the BCM is awake, and 2.5 milliamps when the BCM is asleep. For most BCM functions, the BCM will operate properly
with a system voltage of 9.0-16.0 volts. If system voltages exceed 16.0 volts the BCM will provide protection by disabling certain functions that may
damage due to higher than normal system voltages.
