ally identified by the two heated seat switches
located in the front door trim panels. A second set of
heated seat switches are located in the rear seat cen-
ter console. The front door trim panel mounted
switches control the front seats, while the rear con-
sole mounted switches control the second row seats.
The heated seat system allows the driver, front seat
passenger and 2nd row seat passengers to select from
two different levels of electrical seat heating (HI/LO).
The heated seat system for this vehicle includes the
following major components, which are described in
further detail later in this section:

• Heated Seat Elements - Eight heated seat ele-

ments are used per vehicle, two for each heated seat.
Two heated seat elements are integral to each seat,
one in the seat back and the other in the seat cush-
ion. The rear heated seat cushion elements contain
integral heated seat sensors.

• Heated Seat Modules - Two heated seat mod-

ules are used per vehicle. A Memory Heated Seat
Adjustable Pedal Module (MHSAPM) is mounted
under the drivers seat cushion pan. This module con-
trols the two front heated seats as well as other vehi-
cle functions. A second heated seat module is located
in the 2nd row seat center console and it is used to
control the 2nd row heated seats. (Refer to 8 - ELEC-
TRICAL/ELECTRONIC

CONTROL

MODULES/

MEM/HEAT

SEAT

ADJ

PEDAL

MODULE

DESCRIPTION) for additional information.

• Rear Heated Seat Sensors - Two heated seat

sensors are used per vehicle, one for each rear heated
seat. The heated seat sensors are integral to the rear
heated seat cushion elements. (Refer to 8 - ELEC-
TRICAL/HEATED SEATS/HEATED SEAT SENSOR -
DESCRIPTION) for additional information.

• Heated Seat Switches - Four heated seat

switches are used per vehicle, one for each heated
seat. One switch assembly is mounted in each of the
front door trim panels. The driver side switch assem-
bly is used to control the driver heated seat, power/
memory seat and adjustable foot pedal systems. The
passenger side switch assembly is used to control the

HEATED SEAT SYSTEM

8G - 7

passenger heated seat and power seat systems. The
2nd row heated seat switches are mounted in the 2nd
row seat center console. The 2nd row switches are
used to control the 2nd row heated seat system only.
Refer to heated seat switches later in this section for
additional information. Refer to driver and passenger
seat switches in the Power Seat section for additional
information.

• Door Modules - A door module is concealed

behind the trim panel of each front door. The module
on the driver side is referred to as the Driver Door
Module (DDM), while the module on the passenger
side is the Passenger Door Module (PDM). The DDM
and PDM each utilize integrated circuitry and infor-
mation carried on the Programmable Communica-
tions Interface (PCI) data bus network. In regards to
the front seat heated seat system, the door modules
communicate between the front seat heated seat
switch assemblies and the memory heated seat
adjustable pedal module. The door modules are not
used in the 2nd row heated seat system. (Refer to 8 -
ELECTRICAL/ELECTRONIC

CONTROL

MOD-

ULES/DOOR MODULE - DESCRIPTION) for addi-
tional information.

For complete circuit diagrams, refer to the appro-

priate wiring information. The wiring information
includes wiring diagrams, proper wire and connector
repair procedures, details of wire harness routing
and retention, connector pin-out information and
location views for the various wire harness connec-
tors, splices and grounds.

OPERATION

FRONT SEAT HEATED SEAT SYSTEM OPERATION

The front heated seat system operates on battery

current received through a fuse in the Integrated
Power Module (IPM). Fused ignition switch output
(run-acc) circuits are used, so that the systems will
only operate when the ignition switch is in the On or
Accessory positions. The heated seat system will turn
Off automatically whenever the ignition switch is
turned to any position except On or Accessory. The
Low heat position set point is about 36° C (97° F),
and the High heat position set point is about 41° C
(105° F).

When either of the front heated seat switches are

depressed a resistance signal is sent to the applicable
Door Module (Driver or Passenger). The applicable
Door Module then sends a message via the Program-
mable Communications Interface (PCI) data bus net-
work to the Memory Heated Seat Adjustable Pedal
Module (MHSAPM), signaling the module to energize
the heating element for the selected seat. Light Emit-
ting Diodes (LEDS) in each switch indicate the level

of heat in use. The switch LEDs are controlled by the
applicable Door Module.

The MHSAPM energizes an integral solid-state

relay, which supplies battery current to the seat
heating elements. When high-temperature heating is
selected, the heaters provide a boosted heat level
during the first four minutes of operation after heat-
ing is activated. The heat output then drops to the
normal selected-temperature level. If high-level heat-
ing is selected, the control system will automatically
switch to the low level after two hours of continuous
operation. Operation on the low setting turns off only
when the ignition switch is turned off or the heated
seat switch is pressed a second time indicating an off
command.

The module will automatically turn off the heating

elements if it detects an OPEN or LOW short in the
heating element circuit.

2ND ROW HEATED SEAT SYSTEM OPERATION

The 2nd row heated seat system operates indepen-

dently from the front heated seat system. The 2nd
row heated seat module receives fused battery cur-
rent through the Integrated Power Module only when
the ignition switch is in the ON position. The heated
seat module shares a common ground circuit with
each of the heated seat elements. The heated seat
system will only operate when the surface tempera-
ture of the seat cushion is below the designed tem-
perature set points of the system. The Low heat
position set point is 35° C (95° F), and the High heat
position set point is 40° C (104° F).

A separate heated seat module contains the control

logic for the 2nd row heated seat system. The module
responds to the heated seat switch status, ignition
switch status, and the heated seat element sensor
inputs by controlling the output to the 2nd row seat
heating elements through integral solid-state relays.

When either of the 2nd row seat heated seat

switches are depressed a resistance signal is sent to
the heated seat module, signaling the module to
energize the heating element for the selected seat.

The heated seat sensor provides the heated seat

module with a low-voltage input indicating the sur-
face temperature of the seat cushion. If the surface
temperature is below the temperature set point for
the selected Low or High heated seat switch position,
the module energizes the integral solid-state relay,
which supplies battery current to the heating ele-
ments. When the sensor input indicates the correct
temperature set point has been achieved, the module
de-energizes the solid-state relay. The module will
continue to cycle the solid-state relay as needed to
maintain the temperature set point.

The heated seat system will automatically turn off

whenever the ignition switch is turned to any posi-

8G - 8

HEATED SEAT SYSTEM

HEATED SEAT SYSTEM (Continued)

tion except On. If the ignition switch is turned to the
Off position while a heated seat is ON, the heated
seat will remain Off after the engine is restarted
until a 2nd row seat heated seat switch is depressed
again. This prevents the vehicles battery from being
drained by the heated seat system.

The 2nd row heated seat module also controls the

heated seat LED indicator lamps, located in both of
the 2nd row heated seat switches. The module is pro-
grammed to provide self-diagnostics, if a problem
with the 2nd row heated seat system is detected. If
the module detects faults within the heated seat sys-
tem, it will provide a visual indication of the failure
by flashing the indicator lamps in the appropriate
heated seat switch.

The module will automatically turn off the heating

elements if it detects an OPEN or HI/LOW short in
the sensor circuit, or an OPEN or LOW short in the
heating element circuit. See the owner’s manual in
the vehicle glove box for more information on the fea-
tures, use and operation of the front seat heated seat
system.

DIAGNOSIS AND TESTING - HEATED SEAT
SYSTEM

FRONT SEAT HEATED SEAT SYSTEM DIAGNOSIS

In order to obtain conclusive testing of the front

seat heated seat system, the Programmable Commu-
nications Interface (PCI) data bus circuit must be
checked.

The most reliable, efficient, and accurate means to

diagnose the front seat heated seat system requires
the use of a DRB III

t scan tool and the Appropriate

Diagnostic Information. The DRB III

t scan tool can

provide vital information to the technician trying to
find a problem with the heated seat system. Diagnos-
tic logic is built into the Memory Heated Seat Adjust-
able

Pedal

Module

(MHSAPM)

and

both

door

modules to help locate the problem by the most effi-
cient means possible. Anytime a problem is sus-
pected, a DRB III

t scan tool should be obtained and

used to retrieve any stored fault codes in the
MHSAPM and door modules. If the front heated seat
lights blink the MHSAPM did not respond to the
door modules command to turn on the heated seats.

If diagnostic fault codes are present in the module,

record them on a piece of paper immediately before
proceeding any further. Then, use these fault codes to
identify the problem by verifying the fault code.
Example, If the module records “DRIVER SEAT
HEAT OUTPUT OPEN” fault code, locate the diag-
nostic procedure for this code in the Appropriate
Diagnostic Information and follow the flow chart
until the specific problem is located and resolved.
Once the problem is thought to be corrected, erase

the stored fault code using the DRB III

t scan tool

and verify correct system operation. If the front seat
heated seat system is functioning correctly, verify
that there are no other stored codes in the module
and return the vehicle to service.

If the fault code could not be verified, this is a good

indication that a INTERMITTENT problem may be
present. You must than attempt to find the intermit-
tent problem, such as moving the heating element
within the seat while testing continuity or wiggling
the wire harness/electrical connectors under the seat
while testing continuity. Always, eliminate all other
potential problems before attempting to replace the
MHSAPM or door modules.

For complete circuit diagrams, refer to the appro-

PRELIMINARY TEST

Before testing the individual components in the

heated seat system, check the following:

• Using the DRB IIIt scan tool, check the memory

heated seat adjustable pedal module (MHSAPM) for
any stored fault codes. Record these codes on paper
for reference and resolve using the Appropriate Diag-
nostic Information.

• Check the vehicles battery open-circuit voltage

and charging system performance. If the vehicles
electrical system is defective or weak it may not be
suppling sufficient energy to operate the heated seat
system.

• If the heated seat switch backlighting does not

light with the ignition switch in the On position,
check the fused ignition switch fuse in the integrated
power module. If OK, refer to Heated Seat Switch
Diagnosis and Testing in this section. If not OK,
repair the shorted circuit or component as required
and replace the faulty fuse or repair the open ground
circuit as required.

• If the heated seat switch HI/LO LED indicators

do not light with the ignition switch in the On posi-
tion and the heated seat switch in the Low or High
position, check the fused ignition switch fuse in the
integrated power module. If OK, refer to Heated
Seat Switch Diagnosis and Testing in this sec-
tion. If not OK, repair the shorted circuit or compo-
nent as required and replace the faulty fuse.

2ND ROW HEATED SEAT SYSTEM DIAGNOSIS

The 2nd row heated seat system is capable of per-

forming some self-diagnostics. The following table
depicts the various monitored faults which will be

HEATED SEAT SYSTEM

8G - 9

HEATED SEAT SYSTEM (Continued)

reported to the vehicle operator or technician by
flashing the individual heated seat switch Light
Emitting Diode (LED) indicator lamps. Refer to the
HEATED SEAT SYSTEM SELF-DIAGNOSIS table
below for failure identification. The left side heated
seat switch indicator lamps will flash if a failure
occurs in the left rear heated seat, and the right side
heated seat switch indicator lamps will flash for a
right rear heated seat failure. If a monitored heated
seat system fault occurs, the switch indicator lamps
will flash at a pulse rate of one-half second on, fol-
lowed by one-half second off for a duration of one
minute after the switch for the faulty heated seat is
depressed in either the Low or High direction. This
process will repeat every time the faulty heated seat
switch is actuated until the problem has been cor-
rected.

HEATED SEAT SYSTEM SELF-DIAGNOSIS

Monitored Failure

Switch HI

Indicator Lamp

Switch LO

Indicator Lamp

Heated Seat

Element Shorted

Flashing

Heated Seat

Element Open

Flashing

Off

Heated Seat

Sensor Value Out

of Range

Off

Flashing

Diagnostic logic is built into the 2nd row heated

seat module to help the person trying to locate the
problem by the most efficient means possible. Any-
time a problem is suspected, locate the diagnosis and
testing procedure for the component in question and
follow the steps until the specific problem is located
and resolved. Always eliminate problems in this
order; sensors, wiring, element, switch, switch wir-
ing, heated seat module. Once the problem is thought
to be corrected, verify correct system operation. If the
heated seat system is functioning correctly return the
vehicle to service.

If a problem could not be verified such as not find-

ing anything wrong when following the diagnostic
procedure, this is a good indication that a INTER-
MITTENT problem may be present. You must then
attempt to find the intermittent problem, such as
moving the heating element within the seat while
testing continuity or wiggling the wire harness’s/elec-
trical connectors under the seat while testing conti-
nuity.

FRONT HEATED SEAT SWITCH

DESCRIPTION

The heated seat switch assemblies are mounted in

the left and right side front door trim panels. One
switch assembly is used for each front heated seat.
The two momentary position switches, are incorpo-
rated into one large switch assembly that also
includes other switches. The drivers side switch
assembly (Fig. 1) includes the memory, heat and
power seat switches as well as the adjustable foot
pedal switch. The passenger side switch assembly
includes the power seat and heated seat switches
only. The heated seat switches provide a resistive
multiplexed signal to the appropriate Door Module
through separate hard wired circuits. Each switch
has an Low and High position so that both the driver
and the front seat passenger can select a preferred
seat heating level. Each switch has two Light-Emit-
ting Diodes (LED) which light to indicate that the
heater for the seat is turned on.

The heated seat switches and their LEDs cannot

be repaired. If either switch or LED is faulty or dam-
aged, the entire switch assembly must be replaced.

Fig. 1 CS Driver Heated Seat Switch

1 - Switch Assembly
2 - Driver Heated Seat Switch

8G - 10

HEATED SEAT SYSTEM

HEATED SEAT SYSTEM (Continued)

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