Body Control Module
A Body Control Module (BCM) is concealed behind the driver side end of the instrument panel in the passenger compartment, where it is secured to the fuse panel side of the Junction Block (JB) with 4 screws. See Fig 1 . The JB is the interface between the body, the instrument panel, and the headlamp and dash wire harnesses. The JB also contains the fuses and relays used for the interior electrical system of the vehicle. The BCM is enclosed in a molded plastic housing with two integral external connector receptacles that connect it to the vehicle electrical system through two take outs with connectors from the instrument panel wire harness. See Fig 2 . The BCM also has an integral interface connector concealed on the back side of the unit that joins it through a connector receptacle that is integral to the JB housing to the circuitry within the JB. This connector is referred to as the JB-BCM connector. The combined BCM and JB are sometimes referred to as the Junction Block Module (JBM). There are two different versions of the BCM: base and premium. The base BCM is a subset of the components in the premium version. Basically, the base version BCM does not support the following features: Compass Mini-Trip Computer (CMTC), fog lamps (front and/or rear), Remote Keyless Entry (RKE), remote radio switches, or Vehicle Theft Security System (VTSS). Both versions of the BCM utilize integrated circuitry and information carried on the Programmable Communications Interface (PCI) data bus network along with many hard wired inputs to monitor many sensor and switch inputs throughout the vehicle. In response to those inputs, the internal circuitry and programming of the BCM allow it to control and integrate many electronic functions and features of the vehicle through both hard wired outputs and the transmission of electronic message outputs to other electronic modules in the vehicle over the PCI data bus.
The electronic functions and features that the BCM supports or controls include the following:
- A/C Select Switch Status
The BCM monitors an input from, and transmits the status of the A/C switch on the heater-A/C control. - Ambient Temperature Data
The premium BCM monitors and transmits the ambient temperature sensor input data. - Cargo Lamp Disable
The BCM monitors an input from the cargo lamp switch to provide an interior lighting disable feature. - Chimes
The chime tone generator is located on the ElectroMechanical Instrument Cluster (EMIC) circuit board, but the EMIC goes to sleep with the ignition switch in the Off position. The BCM provides a wake-up output to the EMIC based upon inputs from the key-in ignition switch or the exterior lighting switch, then sends electronic chime request messages to the EMIC for the headlamps on warning and key-in ignition warning. - Door Lock Inhibit
The BCM monitors the key-in ignition switch and the driver side front door ajar switch to provide a door lock inhibit feature. - Exterior Lamp Load Shedding
The BCM provides a battery saver feature which will automatically turn off exterior lamps that remain on after a timed interval. - Exterior Lamp Status
The BCM monitors the status of the park lamp, low beam, high beam or Daytime Running Lamp (DRL - Canada only), front fog lamp (optional), and rear fog lamp (in required markets only) relays. - Exterior Lighting Control
The BCM provides exterior lamp control for standard head and park lamps, as well as Daytime Running Lamps (DRL - Canada only), front fog lamps (optional), and rear fog lamps (in required markets only). This includes support for features including optical horn also known as flash-to-pass) and headlamp time delay. - Flip-Up Glass Control
The BCM monitors the tailgate cylinder lock switch, the tailgate handle switch, the Remote Keyless Entry (RKE) module inputs and the rear wiper switch to provide control for the rear flip-up glass actuator. - Fog Lamp Control
The premium BCM provides fog lamp control for front fog lamps (optional), and rear fog lamps (in required markets only). - Front Wiper System Status
The BCM monitors the status of the front wiper motor park switch. - Fuel Economy And Distance To Empty Calculations
The BCM calculates and transmits the fuel economy and Distance To Empty (DTE) data. - Headlamp Time Delay
The BCM provides a headlamp time delay feature with the ignition switch in the Off position. - Heated Rear Glass Control
The BCM provides control and timer functions for the heated rear glass feature and transmits the system status. - Ignition On/Off Timer
The BCM monitors and transmits the elapsed ignition On timer data and monitors the ignition Off time. - Ignition Switch Position Status
The BCM monitors and transmits the status of the ignition switch. - Instrument Panel Dimming
The BCM monitors and transmits the selected illumination intensity level of the panel lamps dimmer switch. - Interior Lamp Load Shedding
The BCM provides a battery saver feature which will automatically turn off all interior lamps that remain on after a timed interval. - Interior Lighting Control
The BCM monitors inputs from the interior lighting switch, the door ajar switches, the flip-up glass ajar switch, the tailgate ajar switch, the cargo lamp switch, the reading lamp switches, and the Remote Keyless Entry (RKE) module to provide courtesy lamp control. This includes support for timed illuminated entry with theater-style fade-to-off and courtesy illumination defeat features. - Intermittent Wipe And Front Wiper System Control
The BCM monitors inputs from the front wiper and washer switch and the front wiper motor park switch to provide front wiper system control through the wiper on/off and high/low relays. This includes support for adjustable intermittent wipe, mist wipe (also known as pulse wipe), and wipe-after-wash features. - Key-In-Ignition Switch Status
The BCM monitors and transmits the status of the key-in-ignition switch. - Panic Mode
The BCM provides support for the Remote Keyless Entry (RKE) system panic mode feature. - Parade Mode
The BCM provides a parade mode (also known as funeral mode) that allows the interior Vacuum Fluorescent Displays (VFD) to be illuminated at full intensity while driving in daylight with the exterior lamps On. - Power Locks
The BCM monitors inputs from the power lock switches and the Remote Keyless Entry (RKE) module (optional) to provide control of the power lock motors through outputs to the lock, unlock, and driver unlock (RKE only) relays. This includes support for rolling door locks (also known as automatic door locks) and a door lock inhibit mode. - Programmable Features
The BCM provides support for several standard and optional programmable features, including: rolling door locks, headamp time delay interval, Remote Keyless Entry (RKE) driver-door-only or unlock-all-doors, RKE optical chirp, and RKE audible chirp. - Remote Keyless Entry
The premium BCM provides the optional Remote Keyless Entry (RKE) system features, including support for the RKE lock, unlock (with optional driver-door-only unlock, and unlock-all-doors), rear flip-up glass control, panic, audible chirp, optical chirp, and illuminated entry modes, as well as the ability to be programmed to recognize up to 4 RKE transmitters. - Rolling Door Locks
The BCM provides support for the power lock system rolling door locks feature (also known as automatic door locks). - Tailgate And Flip-Up Glass Ajar Status
The BCM monitors and transmits the status of the tailgate and rear flip-up glass ajar switches. - Remote Radio Switch Interface
The premium BCM monitors and transmits the status of the optional remote radio switches. - Self-Diagnosis
The BCM provides support for diagnostics through communication with the DRBIII(R) scan tool over the PCI data bus network. Each analog and digital input can be actuated through the use of this diagnostic protocol. The BCM also stores Diagnostic Trouble Codes (DTCs) to assist in troubleshooting this unit. - Vacuum Fluorescent Display Synchronization
The BCM transmits panel lamp intensity data which allows modules with Vacuum Fluorescent Displays (VFD) to coordinate their illumination intensity. - Vehicle Speed System
The BCM monitors a vehicle speed input from the vehicle speed sensor without Anti-lock Brake System (ABS) or from the Controller Anti-lock Brake (CAB), with ABS, calculates the vehicle speed based upon a programmed axle ratio/tire size (electronic pinion factor), and transmit the vehicle speed information to the Powertrain Control Module (PCM) on a hard wired output circuit. - Vehicle Theft Security System
The premium BCM monitors inputs from the door cylinder lock switches, the tailgate cylinder lock switch, the door ajar switches, the tailgate ajar switch, the flip-up glass ajar switch, the hood ajar switch (in required markets only), and the Remote Keyless Entry (RKE) module to control the features of the optional Vehicle Theft Security System (VTSS).
Hard wired circuitry connects the BCM to the electrical system of the vehicle. These hard wired circuits are integral to several wire harnesses, which are routed throughout the vehicle and retained by many different methods. These circuits may be connected to each other, to the vehicle electrical system and to the BCM through the use of a combination of soldered splices, splice block connectors, and many different types of wire harness terminal connectors and insulators. Many of the electronic features in the vehicle controlled or supported by the BCM are programmable using a customer programming procedure or the DRBIII(R) scan tool. In addition, the BCM software is Flash compatible, which means it can be reprogrammed using Flash reprogramming procedures. However, if any of the BCM hardware components is damaged or faulty, the entire BCM unit must be replaced.