K 3500 Truck 4WD V8-6.6L DSL Turbo VIN 1 (2001)
Body Control Module: Description and Operation
General Description
The Body Control Module (BCM) monitors several inputs in order to arm and disarm the CTD system. The BCM controls the alarm function outputs.
When the BCM detects an unauthorized entry (any door opened), the BCM applies ground to the horn, the park lamp and the headlamp relays. The BCM
will send messages to the security telltale in the instrument cluster through the Class 2 serial data link. The BCM has the following 8 basic modes for
operating the CTD system. The more detailed descriptions are below.
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Off state
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Idle state
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Disarmed state
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Ready-to-arm state
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Arm initiated state
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Arm delay state
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Armed state
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Alarm state
The BCM has the following 6 discrete inputs in order to monitor the CTD system:
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Ignition 1
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Driver door latch (door jamb) switch
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Passenger door latch (door jamb) switch
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Door lock relay
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Door key switch
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Passenger door unlock relay
The BCM applies ground once per second for approximately 2 minutes, or until a valid input to disarm the system is received by the BCM.
Door latch (Door Jamb) Switches
The theft deterrent system uses the door key switch as one method in order to activate the alarm. If the BCM detects any door opening before the
BCM receives a disarm input, the alarm mode activates.
Door Key Switch
The BCM monitors the door key switches in order to disarm the CTD system. When the lock cylinder turns in order to unlock the door, the switch
grounds the disarm input to the BCM.
Remote Control Door Lock Receiver Module System
The remote control door lock receiver module system may also arm and disarm the CTD system. When the remote control door lock receiver receives
a door lock or an unlock signal from the key fob, the remote control door lock receiver sends a message to the BCM. The message orders the BCM to
perform the appropriate door lock/unlock command. The BCM detects the message and performs one of the following functions:
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Locks the doors and enters the armed initiated mode
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Unlocks the doors and enters the ready-to-arm mode
Off State
The CTD system will be in the off state when the ignition switch is in the RUN position and all the doors are closed. The BCM will request the
security telltale to remain OFF.
Idle State
The CTD system will be in the idle state when the ignition switch is in the RUN position and any door is open. The BCM will request the security
telltale to remain OFF.
Disarmed State
The CTD system will be in the disarmed state when the ignition switch is in the LOCK (off) position and all the doors are closed. The BCM will
request the security telltale to remain OFF.
Ready-To-Arm State
The CTD system will be in the ready-to-arm state when the ignition switch is in the LOCK (off) position and any door opens. The BCM will request
the security telltale to flash.
Arm Initiated State
The CTD system will be in the arm initiated state when the ignition switch is in the LOCK (off) position, any door opens, and the BCM detects a lock
command from either the power door lock switch or the remote control door lock receiver. The BCM will request the security telltale to remain ON.
Arm Delay State
The CTD system will enter the arm delay state when the ignition switch is in the LOCK (off) position, the BCM receives a LOCK command from
either the power door lock switch or the remote control door lock receiver and all the doors are closed. The BCM will request the security telltale to
remain ON for 15 seconds.
