Part 3A

EXTERIOR LIGHTING SYSTEM
Exterior Lighting Battery Saver
The BCM monitors the status of and controls the park lamp, head lamp and fog lamp relay's. If any exterior lamps are left on after the ignition is turned OFF, the BCM will turn them OFF after 8 minutes.

Headlamp Delay
The headlamp time delay operates when the ignition switch is turned OFF while the headlamps are still ON. This feature is customer programmable to provide a 30, 60 or 90 second time delay before turning OFF the headlamps. This feature can also be disabled.

Headlamp Switch
The headlight switch on WJ vehicles use a multiplexed (MUX) circuit to the BCM. The BCM Will then control the park lamp, low/high head lamp and fog lamp relay's based on this input.

Fog Lamp Control
The body control module controls the operation of the fog lamp relay which controls the fog lamps. The fog lamps can only be on if the park or low beam headlamps are ON. If the high beams are turned ON, the fog lamps will automatically be turned OFF.

INTERIOR LIGHTING
Courtesy Lamp Control
The body controller has direct control over all of the vehicle's courtesy lamps. The body computer will illuminate the courtesy lamps under any of the following conditions:
1. Any door is ajar and courtesy lamp switch on the left multi-function switch is not in the dome OFF position.
2. The courtesy lamp switch on the left multi- function switch is in the dome ON position.
3. A Remote Keyless entry unlock message is received.
4. Driver door unlocked with key (with VTSS only).

Illuminated Entry
Illuminated entry will be initiated when the customer enters the vehicle by unlocking the doors with the key fob, or with the key if the vehicle is equipped with vehicle theft alarm. Upon exiting the vehicle, if the lock button is pressed with a door open, illuminated entry will cancel when the door closes. If the doors are closed and the ignition switch is turned ON, the illuminated entry also cancels. The illuminated entry feature will not operate if the courtesy lamp switch is in the dome OFF position.

Interior Lighting Battery Saver
If any of the interior lamps are left ON after the ignition is turned OFF, the BCM will turn them OFF after 8 minutes. To return to normal operation, the courtesy lamps will operate after the dome lamp switch or door ajar switch changes state. The glove box, switched reading lamps and vanity lamps require that the ignition be turned to the ON/acc position.

MECHANICAL INSTRUMENT CLUSTER (MIC)
The Mechanical Instrument Cluster (MIC) is divided into 4 sections. Primary gauges, (speedometer and tachometer) secondary gauges, (fuel level, oil pressure, coolant temperature and charging voltage), PCI bus indicator lights and hardwired indicator lights. The gauge mechanisms are all the same, the only difference is the face plate or the physical size of the gauge. The Part Time 4WD indicator, left and right turn signal indicators, and brake warning lamp are hard wired and are not part of any actuator or self test. A "Master Illumination" indicator has been added for the 2001 MY This illuminates any time the park lamps are ON. This indicator is not a part of the self test and does not have a bulb check which is the same for the front fog lamps and high beam indicator. The PCM sends the signals necessary for the cluster to position the gauges. The MIC receives messages directly from the bus and translates them into gauge positions, indicator levels and dimming levels. These messages are received when the ignition is in the "run" or "start" position. The MIL indicator is sent to the MIC from the PCM over the PCI bus. The vacuum fluorescent (VF) odometer/trip and cruise display works with the key in the "run" or "start" positions. The BCM sends dimming level message to the MIC at "key on".

When the ignition is turned "ON" a bulb-check is performed. This consists of activating most of the PCI bus controlled indicator lamps for approximately 2 to 4 seconds.

By holding the "trip/reset" button in while turning the key to the "run" position you can actuate the MIC self test. If the speedometer or tachometer pointer is on the wrong side of the pointer stop, performing the MIC self test will put them in the proper position.

The following lamps are controlled by the PCM (JTEC) over the PCI Bus:
- Low Fuel
- Check Engine
- Trans Over Temp (EATX controlled when equipped)
- O/D OFF (EATX controlled when equipped)
- Cruise

The following lamps are controlled by the BCM over the PCI Bus:
- Front Fog Indicator
- Seatbelt
- High Beam Indicator
- Low Coolant Level

The Instrument Cluster controls the operation of the Seatbelt (for the first 6 to 8 seconds) and the Check Gages lamp. The Anti-Lock Brake Control module controls the operation of the ABS lamp and Brake lamp over the PCI Bus. The Airbag Control Module controls the operation of the Airbag lamp over the PCI Bus. The SKIM controls the operation of the SKIM lamp over the PCI Bus.

If any of the lamps mentioned above do not illuminate during a bulb check or with the DRB III when performing a "self test", inspect the bulb for an open. If the bulb is not open, and the system associated with the lamp operates properly, replace the instrument cluster case assembly.

If any of the lamps mentioned above stays ON after the engine is started, check the system associated with the lamp for diagnostic trouble codes. If no codes are present, and the system associated with the lamp operates properly, replace the instrument cluster case assembly.

Instrument Panel Dimming
I/P dimming is accomplished using the body computer. The panel dimming level switch is read by the body computer which converts the level to a value that is sent over the PCI bus. Other modules such as the Radio, MIC, and the EVIC use this data so their display intensity matches the other incandescent bulbs in the vehicle that are driven directly by the BCM.

MEMORY SEATS
The memory system consists of the driver power seat, both outside rear view mirrors and the radio presets. The memory module for the seat is mounted under the driver's seat. The module is available with or without the heated seat feature. The seat module receives input from the 8-way power seat switch, the driver's seat position sensors, both front seat negative temperature coefficients (NTC's) (if heated seat equipped) and the PCI bus circuit. The memory switch, located on the driver door, is wired directly to the driver door module and sends its messages over the PCI bus. The memory seat module performs the following functions: position the drivers seat, actuate the drivers and passengers seat heaters (if equipped) and sends the memory location over the PCI bus.

When a memory button is pressed (#1 or #2) on the memory switch, the driver door module sends a recall message to the memory seat module (MSM), the PCI radio and the passenger door module. They will in turn position the driver seat, both mirrors and set the radio presets. When the RKE button is pressed, depending on which transmitter (#1 or #2), the passenger door module sends the recall message.

Power Seat
The memory power seat provides the driver with 2 position settings for the driver's seat. Each power seat motor is connected to the MSM with two circuits. Each circuit is switched between battery and ground. By alternating the circuits the MSM controls the movement of the motors based on input from the seat mounted switch.

Each motor contains a potentiometer to monitor the seat position. To monitor the position of the motor, the MSM sends out a 5-volt reference on the sensor supply circuit. The sensor is grounded back to the module on a common ground circuit. Based on the position of the sensor, the MSM monitors the voltage change through the sensor on a separate signal circuit.

The MSM stores the input value of each of the four seat potentiometers in memory when the system is requested. The driver can initiate memory recall, using either the memory switch or the RKE transmitter. When initiated, the MSM adjusts the four seat motors to match the memorized seat position data.

For safety reasons, the memory seat recall is disabled by the MSM when the vehicle is out of park position or if the seatbelt is buckled. Any obstruction to seat movement over a 2 second delay will cause the seat to stop moving in which case a stalled motor would be detected by the MSM which would then flag a trouble code and the corresponding seat output would be deactivated. However, if the object obstructing the seat is removed, the seat will function normally again.

Easy Exit Seat (Available With Memory Seat)
The intent of this feature is to allow for easier entry and exit to the vehicle by moving the seat rearward a short distance when the operator turns the vehicle OFF. The seat can be recalled to one of it's two set memory positions by pressing either of the memory recall buttons on the switch or the RKE transmitters. If any seat movement is initiated, whether manual or by memory recall, after the ignition has been turned OFF, this will cancel any ensuing glide to enter movement until the next ignition cycle.

This feature can be enabled/disabled by the owner through the electronic vehicle information center (EVIC) or using the DRB III. When using the DRB III it will also inform as to what state it is in. To reinstate the feature, simply repeat the process.

Guard Bands
The module provides guard bands which prevent the seat track from hitting the hard limits of the given seat axis during manual power seat operation. The guard band values for each hard limit are stored in EEPROM. The guard band can be by- passed by running the seat to the end of its travel and then releasing the switch and pressing it again. The seat will move a short distance further. Once the seat is past the guard band, it can be stored in memory, but if recall is initiated the seat will move to the guard bands and no further.

When a seat module or seat track assembly is replaced, the DRB III must be used to perform the "Reset Guard Bands" procedure. WARNING: The operator must be out of the seat when this procedure is being used as the seat will move to the end of it's travel in all 8 positions.

Electrically Heated Seats
The heated seat feature is available with or without the memory system. The module is located under the driver's seat and is known as the heated seat module (HSM) or the memory heated seat module (MHSM). The control switches for the heated seats are located on the instrument panel and are wired to the body control module. The BCM then sends the message to the HSM via the PCI bus. The system offers two seat temperature settings of approximately 96.8 °F (36 °C) (LO) and approximately 107.6 °F (41 °C) (HI).

As the temperature in the seat rises, the negative temperature coefficient (NTC) resistance decreases and the voltage reading detected by the HSM decreases. The seat heater output is deactivated once the voltage reading reaches it's threshold for either setting, high or low.

As the temperature decreases, the voltage reading increases until the upper threshold is reached for either setting high or low. At this point the seat heat output is activated once again and this cycle repeats itself as long as the seat heat request is on. The thresholds for low and high settings are preprogrammed into the module memory.

The heated seat switch contain resistors pulled up to 5 volts which are processed by the body control module as the voltage readings indicating desired heat setting high or low.

The heater elements inside the seat back and cushion are different for the Limited and Laredo models. The Laredo seat heater elements are wired in series whereas the Limited seat elements are wired in parallel. This means that if an element is open in a Laredo model there will be no heater output to either the cushion or the seat back. If an element is open in a Limited model, the other elements will operate as usual. However, if one of the elements is open, the seat cushion will have to be replaced.

There are three heater elements in the seat cushions for both models. The Laredo uses a resistor wire for its center and both side bolsters (raised outer side panels) and the Limited uses a carbon fiber element for its center and resistor wire for the bolsters.

SENTRY KEY IMMOBILIZER SYSTEM (SKIS)
The Sentry Key Immobilizer System (SKIS) is an immobilizer system designed to prevent unauthorized vehicle operation. The system consists of a Sentry Key Immobilizer Module (SKIM), ignition key(s) equipped with a transponder chip and engine controller. When the ignition switch is turned ON, the SKIM interrogates the ignition key. If the ignition key is "Valid" the SKIM sends a PCI Bus message to the engine controller indicating the presence of a valid ignition key. Upon receiving a "Valid" key signal the PCM will allow the engine to continue to operate.

SKIS Operation
When ignition power is supplied to the SKIM, the SKIM performs an internal self-test. After the self- test is completed, the SKIM energizes the antenna (this activates the transponder chip) and sends a challenge to the transponder chip. The transponder chip responds to the challenge by generating an encrypted response message using the following:

Secret Key - This an electronically stored value (identification number) that is unique to each SKIS. The secret key is stored in the SKIM, PCM and all ignition key transponders.

Challenge - This is a random number that is generated by the SKIM at each ignition key cycle.

The secret key and challenge are plugged into an algorithm that produces the encrypted response message. The transponder uses the crypto algorithm to receive, decode and respond to the message sent by SKIM. After responding to the coded message, the transponder sends a transponder I.D. message to the SKIM. The SKIM compares the transponder I.D. to the available valid key codes in SKIM memory (8 key maximum). After validating the key the SKIM sends a PCI Bus message called a "Seed Request" to the PCM then waits for a controller response. If the PCM does not respond, the SKIM will send the seed request again. After three failed attempts the SKIM will stop sending the seed request and store a trouble code. If the PCM sends a seed response, the SKIM sends a valid/invalid key message to the PCM. This is an encrypted message that is generated using the following:

VIN - Vehicle Identification Number

Seed - This is a random number that is generated by the PCM at each ignition key cycle.

The VIN and seed are plugged into a rolling code algorithm that encrypts the "valid/invalid key" message. The PCM uses the rolling code algorithm to receive, decode an respond to the valid/invalid key message sent by SKIM. After sending the valid/ invalid key message the SKIM waits 3.5 seconds for a PCM status message from the PCM. If the PCM does not respond with a valid key message to the SKIM, a fault is detected and a trouble code stored.

The SKIS incorporates a warning lamp located in the instrument cluster. The lamp is actuated when the SKIM sends a PCI Bus message to the instrument cluster requesting the lamp ON. The SKIM will request lamp operation for the following:

- bulb check at ignition ON

- to alert the vehicle operator to a SKIS malfunction

For all faults except transponder faults and VIN mismatch, the lamp remains ON steady. In the event of a transponder fault the light flashes at the rate of 1 Hz (once per second). If a fault is present the lamp will remain ON or flashing for the complete ignition cycle. If a fault is stored in SKIM memory which prevents the system from operating properly, the PCM will allow the engine to start and run (for 2 seconds) up to six times. After the sixth attempt, the PCM disables the starter relay until the fault is corrected.

For additional information on the SKIS, refer to the appropriate Powertrain Diagnostic Information.