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Body Control Module: Operation

WARNING: This page is about a different car, the 2005 Dodge Grand Caravan, 2005 Dodge Caravan, and 2005 Chrysler Town & Country. However, it is still accessible from the selected car via links, so may be relevant.

The Body Control Module (BCM) supplies vehicle occupants with visual and audible information and controls various vehicle functions. To provide and receive information, the BCM is interfaced to the vehicle's serial bus communications network, referred to as the Programmable Communications Interface (PCI) bus.

This network consists of the;

  1. Powertrain Control Module (PCM)
  2. Transmission Control Module (TCM)
  3. Mechanical Instrument Cluster (MIC)
  4. Occupant Restraint Controller (ORC)
  5. Compass/Mini-Trip Computer (CMTC)
  6. Electronic Vehicle Information Center (EVIC)
  7. Controller Antilock Brake (CAB)
  8. HVAC Control Module
  9. Sliding Door Control Modules (driver and passenger side doors)
  10. Power Liftgate Module (PLG)
  11. Audio system equipped with RAZ, RBU, RBK, and RBB radios.
  12. Sentry Key Remote Entry Module (SKREEM).
  13. Side Impact Airbag Control Module (SIACM)
  14. Memory Seat Module (MSM)
  15. Sentry Key Immobilizer Module (SKIM)

The BCM is operational when battery power is supplied to the module.

The BCM provides the following features:

  1. Power Door Locks
  2. Automatic Door Locks
  3. Battery Protection - The BCM will automatically turn off all exterior lamps after 3 minutes, and all interior lamps after 15 minutes after the ignition is turned off, if they are not turned off by the driver.
  4. Chime Control
  5. Compass/Mini-Trip support.
  6. Interior Lighting (Courtesy/Reading Lamps)
  7. BCM Diagnostic Reporting
  8. Electronic Liftgate Release (with Power Door Locks)
  9. Exterior Lighting
  10. Headlamp Time Delay (with/without Automatic Headlamps)
  11. Illuminated Entry
  12. Fade to Off Interior Lamps - This feature dims the interior lighting (courtesy lamps) gradually if the BCM does not receive any new inputs that would cause the interior lamps to remain on.
  13. Pulse Width Modulated Instrument Panel Dimming
  14. Door Lock Inhibit - This feature disables the door lock functions if the key is in the ignition and either front door is ajar. Pressing the Remote Keyless Entry (RKE) lock/unlock button under these conditions result in normal lock/unlock activation.

The BCM has the ability to LEARN additional features in the vehicle, provided the appropriate switch input and PCI data bus messages are received. Refer to LEARNED FEATURES .

LEARNED FEATURES

FEATURE  LEARNING KEY 
REAR WIPER CONTROL ON HVAC CONTROL ON INSTRUMENT PANEL PCI BUS MESSAGE RECEIVED FROM HVAC CONTROL
AUTOMATIC HEADLAMPS PCI MESSAGE FROM OVERHEAD OR HEADLAMP SWITCH POSITION (AUTO)
REMOTE KEYLESS ENTRY SKREEM MESSAGE RECEIVED FROM MODULE
FRONT FOG LAMPS HEADLAMP SWITCH POSITION (PARK W/FRONT FOG LAMPS)
POWER SLIDING DOOR PCI IFR RECEIVED FROM MODULE
THE BCM HAS FOUR SWITCH INPUTS FOR THE POWER SLIDING DOOR FEATURE; LOCATED IN THE OVERHEAD CONSOLE ARE THE LEFT AND RIGHT SIDE SLIDING DOOR SWITCHES TO ACTIVATE EITHER OR BOTH SLIDING DOORS UNDER THE PROPER CONDITIONS. ALSO ARE B-PILLAR SWITCHES LOCATED ON THE LEFT AND RIGHT B-PILLAR POSTS.
POWER LIFTGATE PCI IFR RECEIVED FROM MODULE
THE BCM HAS ONE LIFTGATE INPUT LOCATED IN THE OVERHEAD CONSOLE.
POWER LOCKOUT SWITCH INPUT
THE BCM HAS ONE LOCKOUT SWITCH INPUT THAT WHEN ENABLED WILL DISABLE THE B-PILLAR SLIDING DOOR SWITCHES FROM ACTIVATING EITHER SLIDING DOOR WHEN DEPRESSED.
PCI AUDIO SYSTEM PCI MESSAGE RECEIVED FROM MODULE
REMOTE RADIO CONTROLS REMOTE RADIO SWITCHES PRESENT
VEHICLE THEFT SECURITY SKREEM MESSAGE RECEIVED, VALID KEY RECEIVED, & DIAGNOSTIC PID RECEIVED.
MEMORY SEAT AND MIRRORS MEMORY SEAT SWITCH PRESENT AND OR PCI MESSAGE RECEIVED FROM MEMORY MODULE
ABS W/TRACTION CONTROL PCI MESSAGE RECEIVED FROM CAB
SENTRY KEY IMMOBILIZER SYSTEM PCI MESSAGE RECEIVED FROM SKIM OR VTSS PRESENT
ADJUSTABLE PEDAL MODULE PCI MESSAGE RECEIVED FROM ADJUSTABLE PEDAL MODULE (APM)

When replacing a BCM there are three modules available:

  1. Base
  2. Midline
  3. RG - Export

The Midline controller is used on vehicles that have Power Door Locks. If a vehicle is equipped with the Vehicle Theft Security System, the Midline controller becomes a Premium when the theft feature is enabled.

CAUTION: Do not swap Body Control Modules between vehicles or body controller's off the shelf.

The BCM has internal diagnostic capability that assists in diagnosing the system error. When an OPEN or a SHORT circuit exists, the diagnostic tool can be used to read the BCM faults. The faults are very descriptive in identifying the appropriate feature that has faulted.

The only two faults that the BCM logs that conclude the replacement of a BCM are faults;

  1. # 01 - Internal BCM failure (replace BCM)
  2. # 1F - J1850 Internal Hardware Failure (replace BCM)

Otherwise the appropriate diagnostic procedures for each of the features should be taken when the BCM logs a fault.

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