Body Control Module: Description and Operation

The In-Vehicle Multiplexing System, IVMS (LAN system), consists of a BCM (Body Control Module) and five LCUs (Local Control Units). Some switches and electrical loads are connected to each LCU. Some electrical systems are directly connected to the BCM. Control of each LCU, (which is provided by a switch and electrical load), is accomplished by the BCM, via multiplex data lines (A-1, A-2) connected between them.
BCM (Body Control Module)
The BCM, which is a master unit of the IVMS (LAN), consists of microprocessor, memory and communication LSI sections and has communication and control functions. It receives data signals from the LCUs and sends electrical load data signals to them.

Body Control Module (BCM):

The auto amp. for auto air conditioner, if equipped, is built into the BCM. The BCM connectors are located on the front side of the BCM. Do not be confused with the auto amp. connectors on the rear side of the BCM.

NOTE: The auto amp. function has nothing to do with the IVMS.

Local Control Unit (LCU):

LCU (Local Control Unit)
The LCUs, which are slave units of the BCM, have only a communication function and consist of communication LSI and input-output interface circuits. They receive data signals from the BCM, control the ON/OFF operations of electrical loads and the sleep operation, as well as send switch signals to the BCM.

CONTROLLED SYSTEMS
The IVMS controls several body-electrical systems. The systems included in the IVMS are as follows:
^ Power window
^ Power door lock
^ Multi-remote control system
^ Theft warning system
^ Interior lamp (ON-OFF control)
^ Step lamp
^ Illumination (Power window switch illumination)
^ Ignition key warning.
^ Light Warning
^ Seat belt warning
^ Wiper amp.
^ Rear window defogger timer
^ Trouble-diagnosing system
- with CONSULT
- ON-BOARD
Also, IVMS has the "sleep/wake-up control" function. IVMS puts itself (the whole IVMS system) to sleep under certain conditions to prevent unnecessary power consumption. Then, when a certain input is detected, the system wakes itself up. For more detailed information, refer to
"Sleep/Wake-up Control"

Sleep Control:

SLEEP CONTROL
"Sleep" control prevents unnecessary power consumption. About 30 seconds after the following conditions are met, the BCM suspends the communication between itself and all LCUs. The whole IVMS system is set in the "sleep" mode.
^ Ignition switch "OFF"
^ All electrical loads (in the IVMS) "OFF" (except the security indicator lamp)
^ Timer "OFF"

Wake-Up Control:

WAKE-UP CONTROL
As shown above, when the BCM detects a "wake-up" signal, it wakes up the whole system and starts communicating again. The "sleep" mode of all LCUs is now cancelled, and the BCM returns to the normal control
mode. When any one of the following switches are turned ON, the "sleep" mode is cancelled:
^ Ignition key switch (Insert)
^ Ignition switch "ACC" or "ON"
^ Lighting switch (1st)
^ Door switches (all doors)
^ Trunk room lamp switch
^ Hood switch
^ Door unlock sensors (all doors)
^ Also, when key is pulled out of ignition (ignition key switch is turned from ON to OFF), the "sleep" mode is cancelled.

Fail-safe System
Fail-safe system operates when the signal from LCU is judged to be malfunctioning by BCM. If LCU sends no
signal or an abnormal signal to BCM a certain number of times in succession, the IVMS is set in a fail-safe
condition. In the fail-safe condition, no electrical loads on the questionable LCU will operate.