The body control module (BCM) controls the following systems:
• | Battery rundown protection |
• | Various instrument cluster indicators |
• | Exterior and interior lighting control for the following lamps: |
- | Instrument panel lamp dimming |
• | Rear compartment lid release |
• | Theft deterrent (shared with the Passlock sensor and PCM) |
• | Automatic transaxle shift lock control |
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:
• | Headlamps on with ignition off |
• | Park brake engaged with vehicle speed |
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
:
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:
• | Ignition switch actuation |
• | Inadvertent power feedback |
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:
• | 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.