Heated Seat System Description; Diagnosis And Testing - Heated Seat System; Driver Heated Seat Switch Description - Chrysler 300M 2002 Service Manual

LH
HEATED SEAT SYSTEM (Continued)
The heated seat switches are hard wired to the
Body Control Module (BCM). The BCM monitors the
heated seat switch inputs, then sends heated seat
switch status messages to the HSM or MHSM over
the Programmable Communications Interface (PCI)
data bus. The HSM or MHSM contains the control
logic for the heated seat system. The HSM or MHSM
responds to the heated seat switch status messages,
ignition switch status messages, and the front seat
heating element sensor inputs by controlling the out-
put to the front seat heating elements through inte-
gral solid-state relays.
When a seat heater is turned on, the sensor
located on the seat cushion electric heater element
provides the HSM or MHSM with an input indicating
the surface temperature of the seat cushion. If the
surface temperature input is below the temperature
set point for the selected Low or High heated seat
switch position, the HSM or MHSM energizes the
integral solid-state relay, which supplies battery cur-
rent to the heating elements in the seat cushion and
back. When the sensor input indicates the correct
temperature set point has been achieved, the HSM or
MHSM de-energizes the solid-state relay. The HSM
or MHSM will continue to cycle the solid-state relay
as needed to maintain the temperature set point.
The HSM or MHSM and the seat heater elements
operate on non-switched battery current supplied
through the power seat circuit breaker in the junc-
tion block. However, the HSM or MHSM will auto-
matically turn off the heating elements if it detects
an open in the sensor circuit, a short in the heating
element circuit causing an excessive current draw, or
when the ignition switch is turned to the Off posi-
tion.
See the owner's manual in the vehicle glove box for
more information on the features, use and operation
of the heated seat system.
DIAGNOSIS AND TESTING - HEATED SEAT
SYSTEM
Following are tests that will help to diagnose the
components and circuits that are hard wired inputs
or outputs of the heated seat system. However, these
tests may not prove conclusive in the diagnosis of
this system. In order to obtain conclusive testing of
the heated seat system, the Programmable Commu-
nications Interface (PCI) data bus network and all of
the electronic modules that provide inputs to, or
receive outputs from the heated seat system compo-
nents must be checked.
The most reliable, efficient, and accurate means to
diagnose the heated seat system requires the use of a
DRB scan tool and the proper Diagnostic Proce-
dures manual. The DRB III
confirmation that the PCI data bus is functional, that
scan tool can provide
HEATED SEAT SYSTEM 8G - 9
all of the electronic modules are sending and receiv-
ing the proper messages on the PCI data bus, and
that the Heated Seat Module (HSM) or Memory
Heated Seat Module (MHSM) is receiving the proper
hard wired inputs and relaying the proper hard
wired outputs to perform its heated seat system func-
tions.
For complete circuit diagrams, refer to Wiring.
NOTE: DO NOT ATTEMPT TO SWAP MEMORY OR
NON-MEMORY HEATED SEAT MODULES FROM
ONE VEHICLE TO ANOTHER. MOST OF THESE
MODULES ARE VEHICLE FEATURE SPECIFIC AND
THEREFORE NOT INTERCHANGEABLE. ALWAYS
USE THE CORRECT PART NUMBERED MODULE
WHEN DIAGNOSING OR REPLACING A MODULE.
WARNING: REFER
ATTEMPTING ANY
STEERING COLUMN, OR INSTRUMENT PANEL
COMPONENT DIAGNOSIS OR SERVICE. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
PRELIMINARY TEST
Before testing the individual components in the
heated seat system, check the following:
• If the heated seat switch LED indicators do not
light with the ignition switch in the On position and
the heated seat switch in the Low or High position,
check the fused ignition switch output (run) fuse in
the junction block. If OK, refer to Heated Seat
Switch Diagnosis and Testing in this group. If not
OK, repair the shorted circuit or component as
required and replace the faulty fuse.
• If the heated seat switch LED indicators light,
but the heating elements do not heat, check the
power seat circuit breaker in the junction block. If
OK, refer to Heated Seat Element Diagnosis and
Testing in this group. If not OK, replace the faulty
power seat circuit breaker.
DRIVER HEATED SEAT
SWITCH
DESCRIPTION
The heated seat switches are located on the out-
board cushion side shield of the driver and passenger
seats (Fig. 1) (Fig. 2). The two, three-position rocker
type switches provide a resistor multiplexed signal to
the Body Control Module (BCM) through separate
hard wired circuits. Each switch has an Off, Low and
High setting. Each switch contains two light emitting
TO RESTRAINTS BEFORE
SEAT, STEERING WHEEL,