Body Control Module: Description and Operation

OUTLINE
The In-Vehicle Multiplexing System, IVMS (LAN system), Information Bus 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.




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. (Refer to "Warning Buzzer")
- Light warning. (Refer to "Warning Buzzer")
- Seat belt warning. (Refer to "Warning Buzzer")
- Wiper amp. (Refer to "Wiper and Washer")
- Rear window defogger timer. (Refer to "Rear Window Defogger")
- Power window (Refer to "Power Window - IVMS)
- Trouble-diagnosing system

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".





System Diagram





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 LCU's. The whole IVMS is set in the "sleep" mode.
- Ignition switch "OFF"
- All electrical loads (in the IVMS) "OFF"
- Timer "OFF"





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 canceled, and the BCM returns to the normal control mode. When any one of the following switches are turned ON, the "sleep" mode is canceled:
- Ignition key switch (Insert)*
- Ignition switch "ACC" or "ON"
- Lighting switch (1st)
- Door switches (all doors)
- Trunk room lamp switch
- Hood switch
- Driver/passenger side door key cylinder tamper switch
- Driver/passenger side door key cylinder switch
- Trunk lid key cylinder switch
- Multi-remote controller
- 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 canceled.

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.