Description And Operation

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

The Body Control Module (BCM) (1):

• The BCM is the configuration master for the vehicle. As the configuration master, the BCM broadcasts configuration data over the bus whenever the ignition is in the RUN state.
• 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 right kick panel

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

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

• Horn
• Starter relay
• Ignition RUN/START
• 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
• Starter relay

BCM FUNCTION 

Since the BCM separates the branches of the bus networking systems, the BCM must act as a gateway module to allow communication between the different bus networks. The BCM will translate and share messages among all modules on the following bus networks:

• CAN-C
• CAN-Interior High Speed (IHS)
• LIN

The BCM provides the following diagnostic and service features:

• Works as the central gateway to translate and redistribute messages among the CAN-bus networks
• Diagnoses and reports hundreds of Diagnostic Trouble Codes (DTCs)
• Monitors the CAN bus for failures and logs network DTC "U" communication codes
• Supports reprogramming (flashing)
• Houses the vehicle configuration data

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

• Intelligent Battery Sensor
• Steering Wheel Switches (SWS)
• Auxiliary Switch Bank
• Remote Compass Module
• Inside Rearview Mirror

OPERATION CONTROL 

The BCM operates the following functions:

• Exterior lighting
• Ignition control
• Horn
• Door lock control
• Interior Lighting
• Power window operation and function

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

• Headlamp Switch
• Hazard Switch
• Vehicle access point ajar switches
• Interior lamp load detection
• The BCM will also wake-up from module messages from the CAN-C, CAN-IHS, or LIN communication bus networks

STARTING SYSTEM MASTER 

The BCM is the starting system master:

• Uses ignition position bus messages from the Radio Frequency Hub (RF-Hub) 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 RF-Hub 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 on the four-way emergency flashers
3. Press and hold the left steering wheel "up" button for approximately 5 seconds.
4. The vehicle will switch modes.

The modes can be switched back and forth by using this method.

POWER ACCESSORY DELAY:

The BCM manages the Power Accessory Delay (PAD) system for the vehicle.

The PAD feature provides power to some accessory features such as power windows and sunroofs so that they can remain active after the ignition is cycled OFF. This allows the customer to finish closing windows, sun roofs etc. without having to keep the ignition system active. On vehicles equipped with a customer selectable options, the PAD time is programmable. The feature will time out after a specified period of time and is terminated when either front door is opened. PAD does not function when the vehicles ship mode feature is active.