Heated Seats - Jeep 1997 Grand Cherokee Service Manual

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GENERAL INFORMATION
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 7
DESCRIPTION AND OPERATION
HEATED SEAT CONTROL MODULE
HEATED SEAT ELEMENT AND SENSOR . . . . . . 8
HEATED SEAT SWITCH . . . . . . . . . . . . . . . . . . . 7
DIAGNOSIS AND TESTING
HEATED SEAT CONTROL MODULE
GENERAL INFORMATION
INTRODUCTION
Individually controlled electrically heated front
seats are available factory-installed optional equip-
ment on this model. The seat heaters will only oper-
ate when the ignition switch is in the On position,
and the surface temperature at the front seat heating
element sensors is below the designed temperature
set points of the system. The heated seat system will
not operate in ambient temperatures greater than
about 32°C (90°F).
There are separate three-position switches for each
front seat located in the inboard instrument panel
switch pod, just inboard of the steering column. An
Off, Low, or High position can be selected with each
switch, and Light-Emitting Diodes (LED) for each
switch illuminate to give a visual indication that the
system is turned on. The Low heat position set point
is about 32°C (90°F), and the High heat position set
point is about 38°C (100°F). Each switch controls a
Heated Seat Control Module (HSCM) mounted to the
seat cushion frame under each front seat.
When a seat heater is turned on, a sensor located
near the seat cushion electric heater element pro-
vides the HSCM with an input indicating the surface
temperature of the seat cushion. If the surface tem-
perature input is below the temperature set point for
the selected Low or High switch position, a relay
within the HSCM energizes the heating elements in
the seat cushion and back. When the sensor input
indicates the correct temperature set point has been
achieved, the HSCM de-energizes the relay. The
HSCM will continue to cycle the relay as needed to
maintain the temperature set point.
The HSCM will automatically turn off the heating
elements if it detects an open in the sensor circuit, or
a short in the heating element circuit causing an
excessive current draw. The system is also turned off
automatically when the ignition switch is turned to

HEATED SEATS

INDEX
page
HEATED SEAT ELEMENT
HEATED SEAT SENSOR . . . . . . . . . . . . . . . . . . 9
HEATED SEAT SWITCH . . . . . . . . . . . . . . . . . . . 8
. . . . . . . . . 8 HEATED SEAT SYSTEM
REMOVAL AND INSTALLATION
HEATED SEAT CONTROL MODULE
HEATED SEAT SWITCH . . . . . . . . . . . . . . . . . . . 9
. . . . . . . . . 9
the Off position. The control circuit operates on igni-
tion switched battery feed through a fuse in the junc-
tion block. The heating elements operate on battery
feed supplied through the power seat circuit breaker
in the junction block.
Following are general descriptions of the major
components in the heated seat system. Refer to
8W-63 - Power Seat With Heated Seats in Group 8W
- Wiring Diagrams for complete circuit descriptions
and diagrams.
NOTE: This group covers both Left-Hand Drive
(LHD) and Right-Hand Drive (RHD) versions of this
model. Whenever required and feasible, the RHD
versions of affected vehicle components have been
constructed as mirror-image of the LHD versions.
While most of the illustrations used in this group
represent only the LHD version, the diagnostic and
service procedures outlined can generally be
applied to either version. Exceptions to this rule
have been clearly identified as LHD or RHD, if a
special illustration or procedure is required.
DESCRIPTION AND OPERATION
HEATED SEAT SWITCH
The heated seat switch is integral to the inboard
switch pod, which is mounted in the instrument
panel just inboard of the steering column. The two
three-position sliding-type switches, one switch for
each front seat, provide a resistor multiplexed signal
to their respective Heated Seat Control Module
(HSCM). Each switch has an Off, Low, and High
position so that both the driver and the front seat
passenger can select a preferred seat heating mode.
Each switch has a Light-Emitting Diode (LED),
which lights to indicate that the seat heater that the
switch controls is turned on. The heated seat
ELECTRICALLY HEATED SYSTEMS
. . . . . . . . . . . . . . . . . 9
. . . . . . . . . . . . . . . . . . 8
8N - 7
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