K Tahoe 4WD V8-4.8L VIN V (2000)
Body Control Module: Description and Operation
Body Control System Circuit
WAKE-UP STATE
The BCM performs the BCM functions in the wake-up state. The BCM enters the sleep state when the active control or monitoring of system
malfunctions has stopped, or when the BCM is idling.
The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors the BCM inputs during the sleep state, allowing
the BCM to switch between the two states. The BCM wake-ups are as follows:
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Door ajar switches
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Door handle switches
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Dome lamp
^
Park lamps
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Power door lock switches
^
Interior lamp request active
^
Ignition key put into the ignition switch
^
Ignition key removed from the ignition switch
^
Ignition in the RUN position
^
Key in door lock switch
^
RFA request to the BCM
^
Any Class 2 communication requiring BCM interaction.
ASLEEP STATES
The BCM is asleep when the BCM has stopped controlling or monitoring devices and has become idle again. After the ignition switch is turned to the
LOCK position and 20 minutes (1216 seconds) elapse without any Wake-Up signals, the BCM enters into an asleep state and goes into the low power
mode. If the BCM is in low power mode and detects a wake up, the BCM will enter into the wake-up state and enter the high power mode. If the
vehicle has been left inactive (ignition in the LOCK position and no BCM wake-ups) for 20 minutes, the BCM will return to the low power mode.
REMOTE CONTROL DOOR LOCK RECEIVER (RCDLR)
The remote control door lock receiver module is part of the remote keyless entry system. The remote control door lock receiver (RCDLR) module
sends a serial data message to the body control module (BCM) module through a dedicated circuit. The RCDLR module is not on the class 2 serial
data network. The door LOCK and UNLOCK, and Panic Alarm are commands sent to the RCDLR module by the transmitter (Key Fob), the RCDLR
module then sends a serial data message to the BCM to perform the appropriate function.
AMBIENT LIGHT LEVEL SENSOR
The ambient light level sensor has two states, LIGHT and DARK. If the headlamp switch is set to AUTO while in the LIGHT state, the radio, the
PRNDL, and the passenger air bag switch will stay fully bright. If the headlamp switch is set to the PARK LAMP or the HEADLAMP position while
in the LIGHT state, the radio, the PRNDL, and the passenger air bag switch will dim with dimming control. If the headlamp switch is set to the
AUTO, the PARK LAMP, or the HEADLAMP position while in the DARK state, the radio, the PRNDL, and the four wheel drive switch will dim
with the dimming control.
DAYTIME RUNNING LIGHTS AND AUTO HEAD LAMPS
If the headlamp switch is set to the AUTO position while in the LIGHT state, the daytime running lights (DRL) are ON. If the park brake is then set,
the DRLs will turn OFF. When the park brake is RELEASED the DRLs will turn back ON. If the headlamp switch is set to the PARK LAMP position
while in the LIGHT state, the DRLs will be ON and the park lamps will be ON. If the Headlamp switch is set to the HEADLAMP position while in the
LIGHT state, the DRLs will be OFF, the park lamps will be ON and the headlamps will be ON. If the headlamp switch is set to the AUTO position
while in the LIGHT state the and the ambient light level conditions change to DARK for 15 seconds, then the BCM will turn the Headlamps ON.
When the ambient light sensor is in the DARK state the daytime running lights (DRLs) will be OFF regardless of the headlamp switch position. When
the ambient light sensor changes state from DARK to LIGHT the headlamps will turn OFF and the DRL will turn ON after a 20 second delay.
FRONT FOG LAMPS
The front fog lamps are a controlled by the BCM. If the park lamps are ON, the high beams are OFF and the fog lamp switch is pressed, the BCM will
command the fog lamp relay ON. When the BCM senses a momentary low signal on the fog lamp switch circuit, the fog lamps will turn OFF. Toggle
the HIGH/LOW beam switch and the front fog lamps will toggle ON/OFF.
REMOTE PANIC ALARM
The headlamps, park lamps and the horn will be activated after pressing the panic button on the key fob. Press the panic button again to de-activate the
lights and the horn. Pressing the panic button only once on the key fob will activate the headlamps, park lamps, and the horn for 30 seconds or until
the ignition switch is turned to the RUN position.
PASSLOCK(TM) SYSTEM
The Passlock(TM) theft deterrent system is designed to prevent vehicle operation if the correct ignition key is not used to start the vehicle. The
ignition key will allow the lock cylinder to turn, which allows the Passlock(TM) sensor (located inside of the ignition switch assembly) to send a code
to the BCM. If the BCM receives the correct code from the Passlock(TM) sensor the BCM will send a password to the vehicle control module (VCM)
or the powertrain control module (PCM) which will allow the vehicle to start.
