Envoy 2WD V6-4.3L VIN W (1998)
Body Control Module: Description and Operation
Body Control System Operation
Service Precautions
Do not use a test lamp in order to diagnose the BCM electrical system unless you are specifically instructed by diagnostic procedures. Use the J 35616
when diagnostic procedures require probing of connectors. Refer to Special Tools.
The BCM will withstand normal current draws associated with vehicle operations. Avoid overloading any circuit. When testing for opens or shorts, do
not ground or apply voltage to the BCM circuits unless you are instructed to do so. These circuits may only be tested using a J 39200 Digital Multimeter
(DMM) or equivalent. Test electrical circuits using a J 39200 DMM, while the BCM connectors remain connected to the BCM or the recommended
breakout box. Do not remove or apply voltage to the BCM when the ignition switch is in the RUN position. Turn the ignition switch to the LOCK
position before removing or connecting any of the following electrical components:
^
Battery cables
^
Fuses
^
Connectors
Follow the instructions in this section whenever a BCM removal or replacement procedure is performed.
When servicing the BCM system, use the following guidelines:
^
Always DISCONNECT the brown (BRN) BCM connector FIRST.
^
Always CONNECT the brown (BRN) BCM connector LAST.
The BCM may set codes when the ignition switch is in the OFF position.
Disconnecting the electrical connectors from the BCM will set DTC(s).
The BCM may require a 20 minute (1216 second) time period in order to power down when all of the following conditions exist:
^
The ignition switch is turned to the OFF position.
^
The BCM is not receiving any active inputs.
^
The BCM does not receive any active inputs for 20 minutes.
System Description
The BCM is designed in order to perform the following functions:
^
Process various input information
^
Send the needed electrical responses to the other control modules
The input information is related to more than one output. If one input fails, the failure may affect the operation of more than one system.
The BCM controls the operation of the following components:
^
The audible reminders
^
The warnings
^
The power door locks
^
Interior lighting
^
Exterior lighting
The BCM has features that permit the following functions:
^
Timing out and turning OFF inadvertent loads
^
Providing retained accessory power
The BCM is designed in order to interface with a Remote Function Actuator (RFA) subsystem. The interface provides remote operation of certain
features of the vehicle. The BCM also provides vehicle security with an integrated Passlock system.
The BCM communicates via a Class 2 serial data bus. The communication enables diagnosis and programming at the assembly plant or an approved
service center.
The BCM supplies a buffered voltage to various sensors and switches through an internal resistance in the BCM. The resistance is so high in value that
an ordinary test lamp may not light when the lamp is connected to the circuit. An ordinary shop voltmeter may give an inaccurate reading because the
voltmeter input impedance is too low. Use a J 39200 Digital Multimeter (DMM) in order to ensure accurate voltage readings. Refer to Special Tools.
