What does the BCM control?

[1999GMCZ-71]

is it just locks and interior lights, or more like the guage cluster and exterior lights???

[1999GMCZ-71]

nobody knows??

[GnatGoSplat]

It controls:

- Automatic headlights (and parking lights)

- Foglights

- Automatic locks

- Keyless Entry

- Interior Lights

- Factory alarm (and horn)

- Passkey theft deterrent

- Warning chimes

 

That's it off the top of my head.

[JimG]

Off the top of my head (my Helms book is 50 miles from me)

- Instrument Panel/DIC

- Radio (doesn't control it, but it talks to it)

- Automatic climate control (?)

- Horn (2 wires would work, but they like to complicate things)

 

That's all i remember

[Larry]

Here is the official system description straight from the GM service manual

 

 

Body Control System Circuit Description

 

Wake-Up State

Wake-Up signals that will turn the BCM on and cause it to begin active control and/or monitoring certain devices. The BCM wake-ups are:

Door ajar switches

Door handle switches

Dome lamp

Park lamps

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

Liftgate release switch

Liftgate jamb switch

Remote control door lock transmitter request to the BCM

Asleep States

The BCM is Asleep when it 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 a sleep state and goes into the low power mode. If the BCM is in low power mode and detects a wake-up command, 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 Panic Alarm

The head lamps and the horn will be activated after pressing the horn button on the remote control door lock transmitter. Press the horn button again to de-activate the head lamps and the horn. Pressing the horn button only once on the remote control door lock transmitter will activate the head lamps and the horn for 30 seconds or until the ignition switch is turned to the run position.

Battery Run Down Protection

The battery run down protection provides protection against parasitic loads and excessive battery drain and high current loads related to the courtesy lamp circuit. The battery run down protection will also protect the battery against being run down from the courtesy lamp circuit to the level which will not allow the vehicle to start. The BCM will turn off the courtesy lamp circuit after the ignition switch is turned from the run position to the off position and 20 minutes (1216 seconds) have elapsed and without a lamp request input. In order to return the BCM to normal operation once the battery run down protection has shut the interior lamps off, the ignition switch is cycled from off position to the on position.

Inadvertent Power Relay

The BCM turns off inadvertent power relay after 20 minutes (1216 seconds) to preserve battery power. The 20 minute timer starts after any one of the following:

· Ignition switch is turned from run or start to unlock, lock or ACC.

· Illuminated entry is activated

· Interior lamps switch is turned on

· The liftgate is opened or closed

· Underhood lamp is activated

· Vanity lamp is activated

· Courtesy lamp is activated

· Dome lamp is activated

· Glove box lamp is activated

· Reading lamp is activated

· Inside rearview mirror lamp is activated.

If any one of the below inputs occur during the 20 minute timer period, the timer is reset to 20 minutes (1216 seconds).

· Ignition switch is turned from run or start to unlock, lock or ACC.

· Illuminated entry is activated

· Interior lamps switch is turned on

· The liftgate is opened or closed

· Courtesy lamp is activated

· Dome lamp is activated

Retained Accessory Power (RAP)

The RAP feature allows the power windows, the radio and the front and rear wiper systems to be operated after the ignition switch is turned from run position to the lock position, provided that the vehicle's battery voltage is above the minimum voltage threshold when the ignition switch is turned to the off position. The power windows ,radio and the front and rear wiper systems will be turned off when any door is opened or after 10 minutes (599 seconds) have elapsed since the last ignition switch transition.

Illuminated Entry

Interior lights will illuminate for 15 seconds under any of the conditions listed below:

· Open and close the driver's side door

· Open and close the passenger side door

· Open and close a rear passenger door

Interior Illumination

Interior lights will illuminate continuously if the interior light defeat button is off and any door is opened or the liftgate is opened, or if the dimmer switch is rotated to the on position for interior illumination.

Exit Lighting

Interior lights will illuminate for 40 seconds when the ignition key is removed from the ignition cylinder.

Remote Illuminated Entry

Interior lights will illuminate for 40 seconds when the unlock button is pressed on the remote control door lock transmitter or when the liftgate release button is pressed on the remote control door lock transmitter. Interior lights will illuminate for 2 seconds when the lock button is pressed on the remote control door lock transmitter.

Power Door Lock/Unlock Function

The BCM is responsible for energizing the door lock relay. The door lock relay will be energized whenever the BCM receives a command from any of the door lock/unlock switch or a input from the remote control door lock transmitter.

Door Lock/Unlock Switch Function

The drivers door lock switch and the passenger door lock/unlock switches are inputs to the BCM. The BCM will command the door lock relay to unlock the drivers door according to the state of the drivers door lock switch or the passenger door lock switch.

Liftgate Release Function

The liftgate release switch is an input to the BCM. The BCM will command the liftgate to release if the vehicle is in park/neutral or if the park brake conditions are met or if the liftgate release switch is pressed. When the BCM receives a message to activate the liftgate release solenoid from the remote control door lock transmitter, the BCM energizes the liftgate release relay if the vehicle is in park/neutral or if the park brake conditions are met.

Lockout Prevention

The lockout prevention feature is activated when the key is in the ignition switch, any door is opened and then the power lock switch is pressed. This feature will lock the doors then unlock the driver door.

Remote Lock

Press the remote control door lock transmitter lock button once and all doors will lock. Press the remote control door lock transmitter lock button twice within 3 seconds and all doors will lock and the horn will chirp.

Remote Unlock

Press the remote control door lock transmitter unlock button once and the driver door will unlock, the park lamps will flash and the interior lights will turn on. Press the remote control door lock transmitter unlock button twice within 3 seconds and all remaining doors will unlock, the park lamps will flash and the interior lights will turn on. Press the rear button twice within 3 seconds and the liftgate will unlock, the park lamps will flash and the interior lights will turn on.

Audible Warnings

When the BCM determines a driver warning sound is needed, the BCM will sound the chime when applicable.

Key In Reminder

The chime will sound when the ignition switch is not in the run or crank position and the ignition key is in the ignition key cylinder and the drivers door is opened.

Head Lamp Reminder

The chime will sound when the headlamp switch is in the parklamp or headlamp position and the dome lamp switch (thumbwheel) is not at the full down(max dim) position and the ignition switch is in the off position or ACC position. If the dome lamp switch is in the full down position (max dim) and the headlamps are turned on manually and the ignition key is removed the headlamp reminder chime will not sound.

Seat Belt Reminder

The chime will sound for 6 seconds when the ignition switch is turned from the off position to the run position and the seat belt is unfastened. The seat belt telltale on the IPC will also turn ON.

Turn Signal Reminder

The chime will sound when the right or left turn signal is turned on for more than 0.75 miles. The chime will be synchronous with the turn signal flasher.

Driver Warning Telltales

The BCM activates the seat belt telltale on or off in the instrument panel cluster (IPC).

Interior Lighting Control

The BCM can turn on some of the interior lighting independently of the interior lighting system. The vehicles lighting system also can control the same lighting components. The BCM provides the following interior lamp control:

· Courtesy lamps.

· Illuminated entry control of courtesy lamps.

· Vanity mirror lamp is activated

· Courtesy lamp is activated

· Dome lamps

· Glove box lamp

· Reading lamps

· Courtesy lamps are enabled by the following inputs:

· Discrete input to the BCM from the door jamb switches or door handle or dome lamp input

· Remote control door lock transmitter activation (function of illuminated entry)

[MarkD]

Larry,

 

Could you be more specific? LOL!

 

Thanks!

[1999GMCZ-71]

i think that pretty much covers it. Thanks for all the input!