Description And Operation: 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 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 Drivers (HSD)
• Low Side Drivers (LSD)

If an LSD or HSD 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-Interior High Speed (IHS).
  • CAN-Chassis (C).
  • 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 and CAN-IHS.
• 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 (backup data is stored in the Remote Frequency Hub (RF-Hub) module.

LIN MASTER 

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

• IBS - LIN 1.
• Combined Rear View Mirror Module (CRVMM) - LIN 2.
• (LRS) - LIN 2.
• Humidity Sensor - LIN 2.
• Rear View Camera (RVC) Module - LIN 3.
• Hands Free Left and Right Sliding Door Modules (HFM) - LIN 3.
• Hands Free Liftgate Release Module (HFLM) - LIN 3.
• Steering Wheel Switches - LIN 3
• Radio Switches on the back of the steering wheel- LIN 3.

OPERATION CONTROL 

The BCM operates the following functions:

• Exterior lighting including
  • Fog lamps.
  • Turn signals.
  • Daytime Running Lamps (DRL).
  • 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-IHS, LIN communication bus networks.

STARTING SYSTEM MASTER 

The BCM is the starting system master:

• Uses ignition position bus messages from the 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" for approximately 6 to 8 seconds.
4. The vehicle will switch modes.