Body Control System Description. Chevrolet PJJ 2000

For 1990-2009 cars

The body control module (BCM) controls the following systems:

• | A/C compressor

• | Audible warnings

• | Battery rundown protection

• | Various instrument cluster indicators

• | Exterior and interior lighting control for the following lamps:

- | Interior lighting

- | Instrument panel lamp dimming

• | Rear compartment lid release

• | Theft deterrent (shared with the Passlock sensor and PCM)

• | Automatic transaxle shift lock control

• | Keyless entry

• | Rear Defogger

### A/C Compressor Control

The Powertrain Control Module (PCM) and the BCM share the hardware and the software for control of the A/C compressor clutch. The PCM and the BCM communicate this information over the Class 2 serial data line. The BCM receives an A/C request signal from the heater A/C control assembly and transmits this signal to the PCM in order to engage the A/C clutch.

### Audible Warnings

The BCM controls chime requests based upon several inputs to the BCM. The functions which cause the audible warning to be activated by the BCM are listed below:

• | Key-in ignition

• | Headlamps on with ignition off

• | Seatbelt not fastened

• | Park brake engaged with vehicle speed

• | Vehicle in reverse

The BCM sends a class 2 message to the radio when a chime is requested. The radio receives the class 2 message and emits the chime through the right front radio speaker. Chime functions will be inoperative under the following conditions:

• | A loss of class 2 serial data has occured.

• | The factory radio has been replaced with an aftermarket unit.

### Battery Rundown Protection

Battery Rundown Protection helps prevent the battery from deep discharge when you have inadvertently left the interior/courtesy lighting on (rear compartment lid open, door ajar, map light on, etc.). Battery Rundown Protection performs this function by turning off the inadvertent power output. This provides a battery voltage for the interior/courtesy lighting.

Once the ignition switch is turned off, a 20 minute time-out period begins. When the time-out expires, the inadvertent output is turned off. While the inadvertent power output is off, the inadvertent feed back is monitored. If a high to low transition occurs, or if a hardware/software wake up occurs, the inadvertent output is turned back on and the timer is restarted.

### Driver Warning System

The BCM is responsible for interpreting most of the driver warning indicators. The BCM receives inputs sends the following messages to the instrument cluster :

• | SECURITY

• | Low Engine Coolant

• | High Beam

• | SERVICE VEHICLE SOON

• | BRAKE

• | TRACTION OFF

• | CHECK GAGES

### Interior Lighting Control

The interior light control function provides convenience and security by turning on the interior courtesy lights under several conditions. The following conditions enable the courtesy lamps:

• | A discrete input to the BCM from the door ajar switches

• | When you close all doors (The lights stay on for 10 seconds or until you turn on the ignition switch; for the first 2 seconds the courtesy lights are at full intensity, then the lights go to step dim for the remainder of the time.)

• | After the ignition switch has been turned off for less than 2 minutes and either you remove the ignition key or you open the doors (The lights turn on for 10 seconds, or until you turn on the ignition switch, or until you cycle a door jamb switch.)

• | If you use the following features on the remote control door lock transmitter:

- | Activate the door unlock feature

- | Activate the trunk release

When the driver leaves the vehicle (the ignition switch is turned off for more than 2 minutes), the interior lights are first step dimmed, and then theater dimmed to the off state.

### Wake-up/Asleep States

Wake-ups are signals that turn on the BCM and cause the BCM to begin active control and/or monitoring. The BCM wake-ups are as follows:

• | Door ajar switches

• | Ignition switch actuation

• | Inadvertent power feedback

• | Door unlock actuation

• | Trunk release

### Rear Compartment Lid Release

The rear compartment lid release system allows you to release the rear compartment lid by pressing and holding the door unlock button on the remote control door lock transmitter.

In order to operate the rear compartment lid release system, one of the following must be true:

• | The park brake must be set.

• | The transaxle is in PARK.

### Vehicle Theft Deterrent (VTD)

The red SECURITY indicator is a distributed function between the BCM and the instrument cluster. The BCM determines the status of the security indicator based on its internal Passlock® algorithm and what has been communicated to it from the PCM Passlock® algorithm. The BCM then forwards a status of either OFF, ON or FLASH to the instrument cluster over the discrete input circuit 728. If the indicator status is FLASH, the instrument cluster actually controls the flash rate/timing.

The SECURITY indicator is on when the BCM is not in the auto-learn mode and either of the following conditions is true:

• | Any theft deterrent DTC is set

• | The PCM Vehicle Theft Deterrent Fail-Enable bit is true in the last vehicle security status message received.

The SECURITY indicator flashes when either of the following conditions is true:

• | The BCM detects a tamper

• | The PCM Fuel Disable Time-out bit is set in the last vehicle security status message received since the ignition switch was turned to the ON position

If the BCM is in a 10-minute tamper and the ignition switch is turned to the OFF position, the instrument cluster remains awake and flashes the SECURITY indicator until the BCM requests a status of OFF.

### Automatic Transaxle Shift Lock Control

The BCM controls the automatic transaxle shift lock control solenoid by supplying or removing the ground signal to the solenoid when the ignition switch is in the ON position. When the BCM receives a brake switch signal, the BCM disengages the solenoid allowing the transaxle to be shifted out of park.

### Keyless Entry

The BCM and Omrom module control all of the remote keyless entry functions. The Omron module receives a signal from the keyfob, transmits the signal to the BCM and the BCM activates the appropriate output. The BCM controls the following outputs:

• | All door unlock

• | All door lock

• | Rear compartment lid release

### Rear Defogger

When the BCM senses a ground signal from the rear defogger switch, the BCM supplies a ground signal to the rear defogger relay coil. Battery voltage for the relay coil is available with the ignition switch in the ON position from the HVAC fuse. When the rear defogger relay engages, battery voltage is supplied to the rear defogger grid.