Module, Body Control (BCM): Operation

OPERATION 

The Body Control Module (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 relay
• Washer Pump
• Light Emitting Diode (LED) cargo lamps

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 

The BCM will gate messages among all modules on the following bus networks:

• CAN-Chassis (CAN-C)
• CAN-Interior High Speed (CAN-IHS). On this vehicle the CAN-IHS is referred to as the CAN-B
• Local Interface Network (LIN)

The BCM provides the following diagnostic features:

• Diagnoses and reports hundreds of Diagnostic Trouble Codes (DTCs)
• Monitors the CAN bus for failures and logs network DTC "U" communication codes

LIN MASTER  - The BCM is a LIN master module to the following components (if and when equipped):

• Intelligent Battery Sensor (IBS)
• Steering Wheel Switches (SWS) via the Steering Column Control Module (SCCM)
• Light Rain Sensor Module (LRSM)
• Humidity Sensor
• Integrated Center Stack (ICS) module
• Siren
• Intrusion Sensor Transmitter
• Rear Video Camera (RVC)
• Inside Rearview Mirror
• Power Inverter Module (PIM)
• Heated Seat Switches

OPERATION CONTROL 

The BCM operates the following functions:

• Exterior lighting
• Washer and Wiper control
• Ignition control
• Horn
• Power Locks
• Interior Lighting
• Power windows

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

• Headlamp Switch
• Hazard Switch
• Vehicle Access Point (VAP) ajar switches
• Interior lamp load detection
• The BCM will also wake-up from module messages from the CAN-C, CAN-B, 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) module 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 module 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.

Power Accessory Delay (PAD)

The BCM manages the 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.

The BCM stores and compares vehicle configuration data with other ECUs in the vehicle. This process is referred to as Programming Of Configuration of Systems Integrated (PROCSI) (also known as PROXI). If a configuration mismatch is detected, the BCM sets a DTC. A configuration mismatch will require the performance of a Restore BCM PROXI Configuration routine, or a PROXI Configuration Alignment routine using a diagnostic scan tool.

The BCM uses On-Board Diagnostics (OBD) to monitor all of the systems and circuits it controls, then sets active and stored DTC for any monitored system faults it detects. The BCM will also send electronic message requests to the Instrument Panel Cluster (IPC) for the display of certain textual warning messages related to some detected system conditions or faults.