Grand Cherokee 4WD Laredo V8-4.7L (2002)
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: positions the drivers seat, actuates the driver's and passenger's 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 bypassed 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.
