Body Control Module: Description and Operation

System Description
- BCM (Body Control Module) controls the operation of various electrical units installed on the vehicle.

BCM FUNCTION
BCM has a combination switch reading function for reading the operation of combination switches (light, wiper washer, turn signal) in addition to the function for controlling the operation of various electrical components. Also, it functions as an interface that receives signals from the A/C control unit (with manual A/C), A/C auto amplifier (with auto A/C), and sends signals to ECM using CAN communication.

COMBINATION SWITCH READING FUNCTION
1. Description
- BCM reads combination switch (light, wiper washer, turn signal) status, and controls various electrical components according to the results.
- BCM reads information of 20 switches and 5 diagnostic results by combining five output terminals (OUTPUT 1 - 5) and five input terminals (INPUT 1 - 5).

2. Operation description
- BCM outputs battery voltage from input terminals (INPUT 1 - 5) all the time. At the same time output terminals (OUTPUT 1 - 5) activate transistors in turn, and allow current to flow. At this time, if any (1 or more) of the switches are ON, the input terminals corresponding to these switches detect current flow, and BCM judges switches are ON.

3. Example (When fog lamp switch is turned ON)
- When fog lamp switch is turned ON, contact in combination switch turns ON. At this time if OUTPUT 4 transistor is activated, BCM detects current flow in INPUT 5.
- When OUTPUT 4 transistor is ON, BCM detects current flow in INPUTS, and judges fog lamp switch is ON. Then BCM sends fog lamp ON signal to IPDM E/R using CAN communication.
- When OUTPUT 4 transistor is activated again, BCM detects current flow in INPUT 5, and confirms fog lamp switch is continuously ON.

NOTE: Each OUTPUT terminal transistor is activated at 10 ms interval. Therefore, after a switch is turned ON, the electrical loads are activated with a time delay. But this time delay is so short that it cannot be noticed.

4. BCM - Operation table of combination switches
- BCM reads operation status of combination switches by the combination shown in the table.

NOTE: Headlamp has a dual system switch for safe operation.

5. Operation mode
- Combination switch reading function has operation modes shown below.
a. Normal mode
- When BCM is not in sleep mode, each OUTPUT (1 - 5) terminal turns ON-OFF at 10 ms intervals.

b. Sleep mode
- When BCM is in sleep mode, transistors of OUTPUT 1 and 2 stop the output, and BCM enters low-current-consumption mode. OUTPUTS (3 - 5) turn ON-OFF at 60 ms intervals, and receives lighting switch input only.

CAN COMMUNICATION CONTROL
CAN communication is capable of dealing with a lot of information through the two communication lines (CAN L-line, CAN H-line) connecting control units in the system. Also each control unit functions to transmit and receive data, and reads necessary information only.

BCM STATUS CONTROL
BCM changes its status depending on the operation status in order to save power consumption.

1. CAN communication status
- With ignition switch ON, CAN communicates with other control units normally.
- Control by BCM is being operated properly.
- When ignition switch is OFF, switching to sleep mode is possible.
- Even when ignition switch is OFF, if CAN communication with IPDM E/R and combination meter is active, CAN communication status is active.

2. Sleep status
- This is the status to stop CAN communication when ignition switch is turned OFF.
- It transmits sleep request signal to IPDM E/R and combination meter.
- Two seconds after CAN communication with other control unit stops, it switches to CAN communication inactive status.

3. CAN communication inactive status
- With ignition switch OFF, CAN communication is not active.
- With ignition switch OFF, control performed only by BCM is active.
- Two seconds after CAN communication with other control unit stops, it switches to CAN communication inactive status.

4. Sleep status
- BCM is activated with low-current-consumption mode.
- CAN communication is not active.
- When CAN communication operation is detected, it switches to CAN communication status.
- When control performed only by BCM is required by switch, it shifts to CAN communication inactive mode.
- It changes combination switch reading function.

SYSTEMS CONTROLLED BY BCM DIRECTLY
- Power door lock system.
- Remote keyless entry system.
- Power window system.
- Sunroof system.
- Room lamp timer. Refer to "INTERIOR ROOM LAMP".
- Key reminder
- Warning chime
- Turn signal and hazard warning lamps

NOTE: Power supply only. No system control.

SYSTEMS CONTROLLED BY BCM AND IPDM E/R
- Headlamp, tail lamp, fog lamp, auto light system
- Wiper
- Front washer
- Rear window defogger

Major Components And Control System Part 1:

Major Components And Control System Part 2:

CAN Communication System Description
CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN H line, CAN L line) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only.