Description And Operation

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

The Body Control Module (BCM) (1):

• Receives hardwired input from sensors and switches
• Provides logic and output control of certain electrical systems
• Provides load shedding logic and control
• Acts as the central gateway module for the Controller Area Network (CAN) and Local Interface Network (LIN) bus networks
• Supports flashing (reprogramming) of itself
• Is located behind the instrument panel above the left kick panel (1)

Some advantages of the BCM include:

• CAN message optimizations
• Controls all exterior lighting outputs
• Intelligent Battery Sensor (IBS) connection on LIN to BCM
• Interior Lighting and Dimmable "Mood" Lighting
• Light Rain Sensor Module (LRSM) connection on LIN to BCM

OPERATION 

The BCM uses semiconductors or solid-state electronics, including transistors, to perform some of its required functions.

A transistor:

• Is similar to a relay
• Is used to turn an electrical circuit ON or OFF
• Is controlled by another circuit
• Has no moving parts
• Is an integral part of the Electronic Control Unit (ECU) circuit board
• Is often referred to as a "driver"

In the case of the BCM, the following drivers are used to distribute power to various electrical circuits:

• High Side Driver (HSD)
• Low Side Driver (LSD)

If a HSD or LSD is used, it will often be indicated on the wiring diagram by the word "ELECTRONICS" or "PCB" next to a dashed-box inside the ECU.

HSD 

:

• Provides battery voltage (+) to power the load device requiring operation
• Can be used by an ECU to switch power (+) to an electrical circuit, which is typically grounded through its harness and associated circuitry

Some examples of how the BCM uses a HSD include the:

• Horn
• Starter relay
• Ignition Run-Start relay
• Washer Pump

LSD 

:

• Provides a ground (-) for the load device requiring operation
• Can be used by an ECU to switch ground (-) to an electrical circuit, which is typically powered through its harness and associated circuitry

BCM FUNCTION 

• Translates and shares messages among all modules on:
  • CAN-C
  • CAN-CH
  • CAN-IHS
  • LIN (buses 1, 2, 3 and 4)
• Separates the three branches of the system
• Sends and receives electronic messages
• Interchanges messages among the three buses
• Verifies that messages are transmitted in order of priority

The BCM provides the following diagnostic and service features:

• Acts as the gateway between CAN-C, CAN-CH and CAN-IHS
• Works as the central gateway to translate and redistribute messages among the CAN-bus networks
• Diagnoses and reports hundreds of DTCs
• Monitors the CAN bus for failures and logs network DTC "U" (communication) codes
• Supports reprogramming (flashing)
• Houses the vehicle configuration data (backup data is stored in the Radio Frequency Hub Module/RFHM)

LIN MASTER 

- The BCM is a LIN master module to the following LIN slave modules:

• Intelligent Battery Sensor
• Combined Rear View Mirror Module (CRVMM)
• Light Rain Sensing Module (LRSM)
• Humidity Sensor
• Rear View Camera Module (RVCM)
• Hands Free Liftgate Release Module (HFLM)
• Steering Wheel Switches (SWS)

OPERATION CONTROL 

The BCM operates the following functions:

• Exterior lighting including
  • Fog lamps
  • Turn signals
  • Daytime running lamps
  • Park lamps
• Washer/Wiper control
  • Wiper motor
  • Wiper washer
• Ignition control
• Horn
• Door lock control
  • Door lock motors
• Interior Lighting

Several inputs are used to alert the BCM to become active. The hardware wake-up inputs include:

• Headlamp Switch
• Hazard Switch
• Driver Door Ajar
• Passenger Door Ajar
• Left Rear Door Ajar
• Right Rear Door Ajar
• Interior Lamp Load Detection
• The BCM will also wake-up from module messages from the CAN-C, CAN-CH, CAN-IHS, or LIN communication bus networks

STARTING SYSTEM MASTER 

The BCM is the starting system master:

• Uses ignition position bus messages from the RFHM to generate vehicle ignition position (commanded ignition position).
• Works with the Powertrain Control Module (PCM) and various starting system components to start the vehicle.
• Signals the RFHM that the starting attempt has begun or has completed (engine may or may not be running).

MODES OF OPERATION 

Customer Mode:

• All features will work as designed for the customer
• This mode is set by the dealer prior to vehicle delivery

Ship Mode:

• The BCM mode will be set to "Ship Mode" by the Certification test at the end of the vehicle assembly process
  • This mode will be set after all electrical testing is completed and the vehicle is ready to be shipped
• In Ship mode many non-critical vehicle features are disabled, minimizing any unnecessary battery drainage during shipping and storage
• The BCM will broadcast the "Ship Mode" message over the vehicle CAN bus so all other vehicle modules will receive the "Ship Mode" message and respond accordingly

The different BCM operating modes can be changed and verified using the scan tool. In addition to using the scan tool to verify and change the BCM mode, you can set a vehicle to/from Ship Mode by following these steps:

1. Place the ignition in the RUN position.
2. Turn off headlight switch off.
3. Activate the right turn signal.
4. Pull the turn signal stalk toward the driver (highbeam flash simulation) for approximately 10 seconds.
5. The vehicle will switch modes.