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Home >> Jeep Truck >> 2004 >> Liberty 2WD V6-3.7L VIN K >> Repair and Diagnosis >> Body and Frame >> Body Control Systems >> Body Control Module >> Description and Operation >> Functional Operation >> Body Control Module >> Part 1 of 2

Part 1 of 2

The KJ Body Control Module (BCM) is attached to the Junction Block (JB), which is the interface for the Body Harness, Instrument Panel (IP) Harness, and the Headlamp & Dash Harness. The JB also contains the fuses and relays used for the interior electrical system of the vehicle. The combination of the BCM and the JB is called the Junction Block Module (JBM).

There are two versions of JBM's: highline and lowline. The lowline is a subset of the components in the highline. Basically the lowline JBM will not support the following: Front or Rear Fogs, Remote Keyless Entry (RKE), and Vehicle Theft Alarm (VTA). In order to reduce service inventory, only the highline will be stocked. If there is a need to replace a lowline module in the field, a highline module may be used to replace it without any noticeable difference to the customer. The relay content of the JB varies based on vehicle options (power vs. manual seats, with or without Front Fogs, etc.). On right hand drive vehicles there is a separate ground wire connected to the BCM to identify it as a right hand drive.

The BCM controls the following subsystems:
- EVIC
- Door Ajar System
- Exterior Lighting
- Interior Lighting
- Power Door Locks / Remote Keyless Entry
- Rear Window Defogger
- Vehicle Theft Security System
- Windshield Wipers System

The BCM also is involved in the following functions:
- Vehicle Speed Sensing (Program Tire Size)
- Detection / Analysis of Miscellaneous Body Switches
- Driver Information Warnings (Chime)

The BCM is powered via the Ignition Off Draw (IOD) fuse. This allows the BCM to be active whenever the vehicle battery is connected whether the ignition is on or not. This is necessary because the BCM controls functions which are active when the ignition is not on (power locks, VTSS, etc.). If the IOD fuse is removed (i.e. for shipping or storage), the BCM will not be powered when the ignition is off, so any ignition-off functions will not be available. To optimize battery life in a stationary vehicle with the IOD fuse in place, the BCM goes to a low power mode ("sleeps"), when it detects that there is no relevant input or output active when the ignition is off. This transition from full power mode to low power mode, and vice versa, is extremely quick and is transparent to the vehicle owner.

DOOR AJAR SYSTEM
The door ajar, tailgate and flip-up glass ajar states are used as inputs for the Body Control Module (BCM). The BCM uses these inputs to determine exactly what position the doors, tailgate and flip-up glass are in. The DRBIII(R) will display the state of the door ajar, tailgate ajar and flip-up glass ajar switches in Input/Outputs. It's important to note, that when any door, the tailgate or flip-up glass is closed the switch state on the DRBIII(R) will show OPEN. When any door, the tailgate or flip-up glass is open the switch state on the DRBIII(R) will show CLOSED. During diagnosis, if a door, the tailgate or flip-up glass is closed and the DRBIII(R) displays the switch state as CLOSED, it indicates a shorted ajar circuit. If a door, the tailgate or flip-up glass is open and the DRBIII(R) displays the switch state as OPEN, it indicates an open ajar circuit.

The door ajar switch is part of the door latch assembly. Each of the door ajar switches are individually connected to the Body Control Module. On right hand drive vehicles there is a separate ground wire connected to the BCM to identify it as a right hand drive. Therefore, when using the DRBIII and reading Input/Output on a RHD vehicle, the driver door ajar switch will read the Right Front Door Ajar Switch status.

EXTERIOR LIGHTING
The BCM controls the Exterior Lights via the appropriate relays, based on input from the Exterior Light Mode Switch. The BCM reads the position of the Exterior Light Mode Switch, and turns on the corresponding Exterior Lamps. The Exterior Lights are:
- Park Lamps
- Low Beams
- High Beams
- Front Fogs (optional)
- Rear Fogs (export markets)

If the Exterior Lamp Mode Switch is in the Lowbeam position, and then the ignition is turned off, followed by the customer turning off the Exterior Lamp Mode Switch, the BCM enters the Headlamp Delay mode. In this mode, the Lowbeam Lamps are left on for either 30, 60, or 90 seconds. The time period can be changed via the DRBIII(R). This mode is exited if the ignition switch or the Exterior Lamp Mode Switch is cycled.

In certain conditions, the BCM will also control certain Exterior Lamps to signal special conditions (VTSS alarm, etc).

In the Canadian market, the BCM enables the Daylight Running Lamp (DRL) mode. The High-beam Relay is replaced in the JB with a solid-state relay. The BCM will duty cycle this relay when the engine is running and the Lowbeam Lamps are not on.

If either the Exterior Lamps are left on with the ignition in the OFF position for greater than 8 minutes, the BCM will turn off ("Loadshed") the lamps until another cycle occurs (i.e. ignition is turned on, Exterior Lamp Mode Switch position is changed, etc.). This feature exists to attempt to save the vehicle battery in the event that a customer forgets to turn off the headlamps, etc. On export vehicles, the park lamps do not "Loadshed".

INTERIOR LIGHTING
The BCM controls the Courtesy Lamps directly based on input from the Dimmer Switch, Door Ajar switches. Glass Ajar switch, and Rear Courtesy Disable switch.

The Courtesy Lamps are switched on in the event of a door or glass ajar, RKE unlock reception, or optional cylinder lock switch in the unlock position event. Upon the above inputs returning to off (door closed, etc.) the Courtesy Lamps will stay on for 27 seconds, and then fade to off ("Theater Dimming") over a period of 3 seconds.

If the Dimmer Switch is turned to the off position, the Courtesy Lamps are disabled and will not be turned on when any of the above inputs occur.

If the Rear Courtesy Disable Switch is in the disable position, the Courtesy Lamps will still be turned on when any of the above inputs occur except the flip-up glass ajar or tailgate ajar. This allows the interior lights to be off if the customer leaves the tailgate open for an extended period of time ("Tailgate Mode").

If the ignition is turned to Run, or a RKE door lock input is received while the Courtesy Lamps are on, the remainder of the 27 second timer is skipped and the Courtesy Lamps proceed immediately to the 3 second fade to off mode.

There are also two Map Lamps in the vehicle headliner between the driver and the passenger. The Map Lamps may be individually controlled independently of the Courtesy Lamp function. The Map Lamps are turned off and on by pressing directly on the lens cover. If the Map Lamp is in the OFF position, the Map Lamps will mimic the Courtesy Lamp state (i.e. if the Courtesy Lamps are on, the Map Lamps will also be on). If the Map Lamp is in the ON position, the Map Lamp will remain on until it is pressed again by the driver (independent of the Dimmer switch, door ajars, etc.).

If either the Courtesy Lamps or the Map Lamps are left on with the ignition in the OFF position for greater than 8 minutes, the BCM will turn off ("Loadshed") the lamps until another cycle occurs (i.e. ignition is turned on, a different door is opened, etc.). This feature exists to attempt to save the vehicle battery in the event that a door is accidentally left open, etc.

OVERHEAD CONSOLE

ELECTRONIC VEHICLE INFORMATION CENTER (EVIC)
When equipped, the Electronic Vehicle Information Center (EVIC) is located in the overhead console. The EVIC supplements the standard vehicle instrumentation. The EVIC also provides additional driver information, warnings and an interface to enable and disable vehicle programmable features and displays memory system messages. Most of the EVIC display information is received over the PCI bus. The EVIC sends and receives data over the PCI bus, communicating with the BCM, PCM, and the Instrument Cluster.

The EVIC uses a vacuum fluorescent (VF) display to supply the vehicle operator with a compass heading, outdoor temperature, average fuel economy, miles to empty, miles to service, tire pressure (if equipped), trip odometer, and elapsed ignition on time.

The EVIC function buttons are labeled C/T, RESET, STEP, and MENU.

The optional Universal Garage Door Opener (UGDO) known as HomeLink(R) is integrated with the EVIC. The three UGDO buttons are labeled with dots to indicate the channel number.

VEHICLE INFORMATION DISPLAY
The EVIC provides the following functions:
- Compass direction
- Outside temperature
- Elapsed ignition on time
- Distance to empty
- Average fuel economy
- Trip Odometer
- Service Interval
- Customer Programmable Features
- Tire Pressure (if equipped)
- Vehicle Information Warning Message Displays

The EVIC will not display information for any of the screens for which it did not receive the proper PCI bus data. Refer to the symptom list in the Compass Mini-Trip Computer section for problems related to the EVIC.

The EVIC receives the following messages from the Instrument Cluster:
- Low Washer Fluid
- Turn Signal On
- Vehicle Odometer

The EVIC receives the following message from the BCM;
- Door(s) Ajar
- Reargate Ajar
- Liftglass Ajar
- Remote Key Battery Low
- VF display dimming brightness and exterior lamp status
- Elapsed Ignition On Time data
- Distance to Empty
- Average Fuel Economy
- Trip Odometer data
- Tire Pressure Data
- Verification of US/Metric status

The EVIC receives the following message from the PCM:
- Filtered Outside Temperature
- Vehicle Speed
- Engine RPM
- Charging System Voltage

WARNING MESSAGES: When the appropriate conditions exist, the EVIC displays the following warning messages and symbols. Each message is accompanied by a series of beeps.

- TURN SIGNAL ON (with graphic)
- PERFORM SERVICE
- DRIVER DOOR OPEN (with graphic)
- PASSENGER DOOR OPEN (with graphic)
- DOOR(S) OPEN (with graphic) N DOORS OPEN (N=2, 3, 4)
- REARGATE OPEN
- LIFTGLASS OPEN
- HOOD OPEN (BUX Only)
- WASHER FLUID LOW
- REMOTE KEY BATTERY LOW
- NO J1850 MSGS RECEIVED
- LOW TIRE PRESSURE WARNINGS

CUSTOMER PROGRAMMABLE FEATURES:
Press the MENU button to select one of the following displays:

- LANGUAGE (Press STEP button to select one of 5 languages)
- US or METRIC (Press STEP button to toggle between US or Metric units)
- AUTO DOOR LOCKS (Press STEP button to select 'Yes" or "No.") (EXCEPT BUX)
- AUTO UNLOCK ON EXIT (Press STEP button to select "Yes" or "No.") (EXCEPT BUX)
- REMOTE UNLOCK DRIVER'S DOOR 1st (Press STEP button to select)
- SOUND HORN ON LOCK (Press STEP button to select) (except BUX)
- FLASH LIGHTS ON LOCK/UNLOCK? (Press STEP button to select "Yes" or "No.")
- HEADLAMP DELAY (Press STEP button to select desired delay)
- SERVICE INTERVAL (Press STEP button to select distance intervals)
- RESET SERVICE DISTANCE (Press STEP button to select "Yes" or "No.")
- TRAIN REMOTE (Press STEP button to select "Yes" or "No.")
- LOW FUEL CHIME (Press STEP button to select "Yes" or "No.")
- RETRAIN TIRE SENSORS (Press STEP button then MENU button to start)

STEP BUTTON
The EVIC will enter a traveler screen by pressing the STEP button while the Compass/Temp screen is displayed or by stepping through all the personalization screens with the MENU button. The STEP Button can be used in one of the following ways:

1. To sequentially select one of the 5 displays or blank display in the following order:
- Average Fuel Economy
- Distance to Empty
- Trip Odometer
- Time Elapsed
- Service Mileage
- Off (Blank)

2. To set the magnetic variance zone when VARIANCE = X (X = 1 - 15) is indicated the VF display.
3. Pressing the STEP button while displaying a personalization screen will toggle the options for that feature.

RESET BUTTON
The RESET Button has two different functions:
1. To clear the trip functions that may be reset
2. To enter and exit the diagnostic mode
Pressing the RESET button once will clear the trip function that is currently being displayed and the EVIC will send a PCI bus beep request to the BCM. If the RESET button is pressed again within 3 seconds, the EVIC will reset ALL of the reset table trip functions and an additional beep request is sent to the BCM. The trip functions that may be reset are:
- Average Fuel Economy
- Trip Odometer
- Elapsed Time

A reset will only occur if one of the trip functions that may be reset is currently being displayed. The EVIC module will send a beep request to the BCM.

Simultaneously pressing the RESET button and the C/T button while turning the ignition from Off to On will enter the EVIC into the self-diagnostic mode. The EVIC self-diagnostic mode may also be initiated using the DRBIII(R).

COMPASS/TEMPERATURE (C/T) BUTTON
Pressing the Compass/Temperature Button (C/T) will cause the EVIC to display the compass and temperature information. This function will operate from a traveler display. The EVIC simultaneously displays the compass reading and the outside temperature. Outside temperature information is received via the PCI bus from the BCM.

The EVIC module internally senses and calculates the compass direction.

TRAVELER DISPLAY FUNCTIONS
Using the STEP button will change the EVIC between modes of operation and display the appropriate information according to data received from the PCI Bus.

COMPASS OPERATION
Upon ignition on, if the calibration information stored in the EVIC memory is within the normal range, the EVIC will perform in slow Auto-Cal mode. In slow Auto-Cal mode, the EVIC continuously compensates for the slowly changing magnetic field of the vehicle. The compass module detects changes in the vehicle magnetism and makes appropriate internal corrections to ensure proper displayed direction.

However, if the calibration information stored in the EVIC memory is not within the normal range at ignition on, the EVIC will enter fast Auto-Cal. CAL is displayed along with the temperature.

Auto activation of the fast Auto-Cal mode will also occur when the EVIC is subjected to high magnetic field strength levels, which cause all compass readings to be erroneous for a continuous period of five (5) minutes. During fast Auto-Cal, CAL will be displayed along with the temperature.

Fast Auto-Cal can also be performed manually, by pressing and holding the RESET button for 10 seconds during the Compass/Temperature display mode.

SETTING MAGNETIC ZONE VARIANCE
Variance is the difference between magnetic North and geographic North. For proper compass function, the correct variance zone must be set. Refer to the Zone Variance map for the correct zone. Follow these steps to check or change the variance zone:
- The ignition switch must be in the On position and the EVIC display must not be blank
- If the compass/temperature data is not currently being displayed, momentarily press and release the C/T button to display compass/temp information.
- Press and hold the RESET button until VARIANCE = XX is displayed. The EVIC will display the variance zone stored in memory and the word VARIANCE.
- Use the STEP button to select the proper variance zone number, 1 through 15.
- After selecting the proper zone number, momentarily press and release the RESET button. The variance zone is then stored in the memory and the EVIC returns to normal operation.





COMPASS CALIBRATION
The compass module has 2 types of auto-calibration; slow-cal and fast-cal. Slow-cal ensures that during normal vehicle operation the compass performs auto-calibration functions to keep the compass sensors in their proper operating range. Whenever the ignition is On and the EVIC receives PCI bus data indicating that engine RPM is greater than zero, auto-calibration is performed continuously.

If the calibration information stored in the compass module memory is not within the normal range after a power-up cycle, the compass will display CAL. The EVIC will enter into the fast-cal mode until calibration is complete.

To enter the compass into Manual Calibration mode, perform the following steps:
- Drive the vehicle to an area away from any large metal objects or overhead power lines.
- Ensure that the proper variance zone is selected. See "Setting Magnetic Zone Variance."
- The ignition switch must be in the On position and the EVIC display must not be blank.
- Press the C/T button to view the Compass/Temperature display.
- Press and hold the RESET button until CAL is displayed, then release the button.
- Drive slowly, less than 5 MPH (8KPH) in at least 1 complete 360 degree circle.
- CAL will remain illuminated to alert the driver that the compass is in the calibration mode.
- After calibration is complete, CAL will turn off.

If the compass appears blank, unable to be calibrated, or the compass displays false indications, the vehicle must be demagnetized.

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