Jeep 1997 Grand Cherokee Service Manual page 540

8N - 8 ELECTRICALLY HEATED SYSTEMS
DESCRIPTION AND OPERATION (Continued)
switches and their LED cannot be repaired. If either
switch or LED is faulty, the inboard switch pod unit
must be replaced.
HEATED SEAT CONTROL MODULE
The Heated Seat Control Module (HSCM) is an
electronic thermostatic module designed to operate
the electric seat heater elements. Two modules are
used in the vehicle, one for each front seat. The
HSCM for each seat is mounted to a bracket under
the seat cushion spring. The bracket is secured to the
inside surface of the outboard seat cushion frame
with a single screw driven through the frame from
the outside.
Inputs to the module include the multiplex resistor
instrument panel switch signals (which includes the
seat cushion temperature sensor circuits), an igni-
tion-switched battery feed, a non-switched battery
feed, and a ground. The only HSCM output is the
feed for the seat heating elements.
The HSCM cannot be repaired and, if faulty, it
must be replaced.
HEATED SEAT ELEMENT AND SENSOR
Two heated seat heating elements are used in each
front seat, one for the seat cushion and the other for
the seat back. The two elements for each seat are
connected in series with the HSCM.
The temperature sensor is a Negative Temperature
Coefficient (NTC) thermistor. One temperature sen-
sor is used for each seat, and it is integrated into the
seat cushion heating element.
The heating elements are sewn into the seat cush-
ion cover and seat back cover assemblies, which are
serviced individually. The heating elements and tem-
perature sensor cannot be repaired and, if faulty, the
affected seat cover assembly must be replaced. Refer
to Group 23 - Body for the seat cover service proce-
dures.
DIAGNOSIS AND TESTING
HEATED SEAT SYSTEM
For circuit descriptions and diagrams, refer to
8W-63 - Power Seat With Heated Seats in Group 8W
- Wiring Diagrams.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO
RESTRAINT SYSTEMS
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
GROUP 8M - PASSIVE
BEFORE ATTEMPTING
STEERING COLUMN,
Before testing the individual components in the
heated seat system, check the following:
• If the heated seat switch LED doesn't light with
the ignition switch in the On position and the heated
seat switch in the Low or High position, check the
fuse in the junction block. If the fuse is OK, test the
heated seat switch as described in this group.
• If the heated seat switch LED lights, but the
heating elements don't heat, check the circuit
breaker in the junction block. If the circuit breaker is
OK, test the heated seat elements as described in
this group.
HEATED SEAT SWITCH
For circuit descriptions and diagrams, refer to
8W-63 - Power Seat With Heated Seats in Group 8W
- Wiring Diagrams.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER
RESTRAINT SYSTEMS
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the inboard switch pod as described in
this group. Unplug the 10-way wire harness connec-
tor from the switch pod. Check for continuity
between the ground circuit cavity of the 10-way
switch pod wire harness connector and a good
ground. There should be continuity. If OK, go to Step
3. If not OK, repair the open circuit as required.
(3) Connect the battery negative cable. Turn the
ignition switch to the On position. Check for battery
voltage at the fused ignition switch output circuit
cavity of the 10-way switch pod wire harness connec-
tor. If OK, go to Step 4. If not OK, repair the open
circuit as required.
(4) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Unplug the remaining inboard switch pod wire har-
ness connectors and remove the inboard switch pod
from the instrument panel.
(5) With both heated seat switches in the Off posi-
tion, check for continuity between the fused ignition
switch output circuit terminal and the driver heated
OR
seat switch output circuit terminal in the 10-way
connector receptacle on the back of the inboard
switch pod. Repeat this check between the fused igni-
tion switch output circuit terminal and the passenger
heated seat switch output circuit terminal. In each
TO GROUP 8M -
BEFORE ATTEMPTING
STEERING COLUMN,
ZG
PASSIVE
OR