BODY CONTROL MODULE (GRAND CHEROKEE)
Body Control Module (BCM) is located under left side of dash. BCM controls many of the vehicle's electrical functions and features by providing power or ground to a variety of systems. BCM contains a central processing unit and interfaces with other modules in the vehicle on the PCI data bus network.
BCM is the only module that has the capability of providing both "bias" and "termination" on the PCI bus system. See PCI BUS SYSTEM (GRAND CHEROKEE) . Systems are monitored by BCM through voltage drops.
CCD BUS SYSTEM (CHEROKEE & WRANGLER)
The Chrysler Collision Detection (CCD) bus is a pair of twisted wires traveling from module-to-module receiving and delivering coded information. The code identifies the message and its importance. When multiple messages attempt to access CCD bus at once, code assigns priority ranking.
The 2 twisted wires used by the CCD bus system are called bus "+" (positive) and bus "-" (negative). Both wires carry approximately 2.5 volts. The network consists of some modules with "bias" and some with "termination".
Bias is the part of the voltage divider network that places both bus "+" and bus "-" at 2.5 volts. Termination is the part of the circuitry required to complete the voltage divider network and also provide some electromagnetic protection for the CCD bus. Terminations in all CCD applications have approximately 120 ohms resistance.
COMPASS/MINI-TRIP COMPUTER (CMTC)
Compass/mini-trip computer consists of a mini/trip computer module, electronic compass and thermometer. Compass/mini-trip computer module is self-calibrated and requires no adjustment.
INSTRUMENT CLUSTER
Instrument cluster includes a speedometer, tachometer, fuel gauge, oil pressure gauge, water temperature gauge, voltmeter and a series of warning lights.
Powertrain Control Module (PCM) sends signals necessary for instrument cluster to position gauges. Instrument cluster receives these messages from bus and translates them into gauge positions. BCM sends status of all indicator lights and dimming level to instrument cluster over bus when ignition switch is in RUN or START positions. Malfunction indicator light (CHECK ENGINE) status is sent to BCM from PCM over bus. Vacuum florescent odometer/trip display works when ignition switch is in RUN or START positions. BCM stores mileage information that odometer displays. If bus is not functioning, odometer will display dashes instead of the mileage. BCM sends mileage message and dimming level message to vacuum fluorescent display when ignition switch is in the RUN position. All other instrument cluster features only work when the ignition switch is in the RUN position.
ANTI-THEFT SYSTEM
Note. Anti-theft system may also be referred to as Vehicle Theft Security System (VTSS).
Anti-theft system monitors vehicle doors, ignition switch, power door locks and door key cylinder switches to determine if alarm should trigger and prevent engine from starting. When an unauthorized entry is detected, system responds by sounding horn, flashing headlights, flashing taillights and flashing parking lights for 3 minutes. BCM also sends a message to PCM to prevent engine from starting.
System can be armed by using remote keyless entry transmitter or by pressing power door lock switch when exiting vehicle. Anti-theft system uses a security light located above instrument cluster to indicate when system is armed. System can be disarmed by unlocking a front door, liftgate or by remote keyless entry transmitter. If vehicle is tampered with anti-theft indicator light will change from a slow steady flash to a quick double flash and horn chirp will not function when unlock command is received from remote keyless entry transmitter.
Panic alert mode flashes headlight and taillights, pulses horn and disarms alarm. Driver can exit panic alert mode by either pushing panic button on remote keyless entry transmitter or by driving vehicle above 15 MPH.
Whenever BCM is replaced, anti-theft system must be enabled by unlocking doors with key one time or by using scan tool. This allows BCM to see that the vehicle is equipped with an anti-theft system.
DOOR MODULES
Door modules are used to reduce wiring complexity, and to facilitate faster and easier diagnosis. One door module is located in each front door. Door modules control power door locks, driver window express down, memory recall functions for memory seats and mirrors, keyless entry system and power mirrors.
PCI BUS SYSTEM (GRAND CHEROKEE)
The Programmable Communication Interface (PCI) bus system consists of a single wire. The BCM acts as a splice to connect each module and Data Link Connector (DLC). Each module uses its local ground as bus reference. If more than one module is trying to access the PCI bus at one time, code being sent determines which message has higher priority, and is then allowed to access bus first. Communication over the bus is essential to proper operation of vehicles on-board diagnostic systems and DRB. Problems with operation of bus or DRB must be corrected before proceeding with diagnostic testing. See appropriate VEHICLE COMMUNICATIONS article.
POWER WINDOWS
Power windows can be raised or lowered from driver's door module or individual door switch. Driver's door module has a lockout switch that prevents windows from being operated from any switch except driver's door. When this switch is pressed, it also shuts off individual door switch LEDs.
POWER DOOR LOCKS
When lock button on remote keyless entry transmitter is pressed, all doors will lock, illuminated entry will turn off and anti-theft system will arm. When transmitter unlock button is pressed one time, left front door will unlock, illuminated entry will turn on and anti-theft system will disarm. When transmitter button is pressed a second time, all other doors will unlock.
Passenger's door module contains remote keyless entry receiver. When passenger's door module receives a valid signal from remote keyless entry transmitter, it will send a signal on the bus to lock or unlock doors. Remote keyless entry transmitter uses radio frequency signals to communicate with remote keyless entry receiver.
WIPER SYSTEM
Wiper system provides driver with normal wipe (low and high speeds), intermittent wipe, wipe after wash and pulse wipe functions. Low and high speeds are directly controlled by multifunction switch. Intermittent wiper function is controlled through intermittent wiper relay and BCM. BCM uses vehicle speed input to double normal delay times when vehicle speed is less than 10 MPH.