Heated Seat System Description; Operation; Diagnosis And Testing - Heated Seat System - Chrysler 300M Service Manual

8G - 10 HEATED SEAT SYSTEM
HEATED SEAT SYSTEM (Continued)
The heated seat system also relies upon resources
shared with other components in the vehicle over the
Programmable Communications Interface (PCI) data
bus network. The PCI data bus network allows the
sharing of sensor information. This helps to reduce
wire harness complexity, internal controller hard-
ware, and component sensor current loads. At the
same time, this system provides increased reliability,
enhanced diagnostics, and allows the addition of
many new feature capabilities. For diagnosis of the
heated seat system or of the PCI data bus network,
the use of a DRB III scan tool and the proper Diag-
nostic Procedures manual are recommended.
Following are general descriptions and operations
of the major components in the heated seat system.
See the owner's manual in the vehicle glove box for
more information on the features, use and operation
of the heated seat system. Refer to Wiring for the
location of complete heated seat system wiring dia-
grams.

OPERATION

The heated seat system will only operate when the
ignition switch is in the On position, and the surface
temperature at the front seat heating element sen-
sors are below the designed temperature set points of
the system. The heated seat system will not operate
in ambient temperatures greater than about 41° C
(105° F). The heating elements, sensors and the
heated seat switches are hard wired to the Memory
Heated Seat/Mirror Module (MHSMM).
The MHSMM contains the control logic for the
heated seat system. The module responds to the
heated seat switch status, ignition switch status, and
the seat heating element sensor inputs by controlling
the output to the front seat heating elements through
integral solid-state relays.
When a seat heater is turned on, the heated seat
sensor located in the seat cushion heating element
provides the module with an input (low-voltage) indi-
cating the surface 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
elements in the seat cushion and seat back. 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 Low heat position set
point is about 36° C (97° F), and the High heat posi-
tion set point is about 41° C (105° F).
The module and the heated seat elements operate
on non-switched battery current supplied through the
power seat circuit breaker in the junction block. The
module will automatically turn off the heating ele-
ments if it detects an open or a HI/LOW short in the
sensor circuit, or a open or LOW short in the heating
element circuit.
DIAGNOSIS AND TESTING - HEATED SEAT
SYSTEM
In order to obtain conclusive testing of the heated
seat system, the Programmable Communications
Interface (PCI) data bus circuit must be checked.
The most reliable, efficient, and accurate means to
diagnose the heated seat system requires the use of a
DRB III scan tool and the Service and Body Diag-
nostic Procedures Manuals. The DRB III scan tool
can provide vital information to the technician trying
to find a problem with the heated seat system. Diag-
nostic logic is built into the memory heated seat/mir-
ror module to help the person trying to locate the
problem by the most efficient means possible. Any-
time a problem is suspected, a DRB III
must be obtained and used to retrieve any stored
fault codes in the memory heated seat/mirror mod-
ule. If diagnostic fault codes are present in the mod-
ule, 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, locate the diagnostic
procedure for this code in the appropriate Body Diag-
nostic Procedures Manual 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
and verify correct system operation. If the 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, such as not
finding anything wrong when following the diagnos-
tic flow chart in the Body Diagnostic Procedures
Manual. This is a good indication that a INTERMIT-
TENT problem may be present. You must than
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. Always, eliminate all other potential problems
before attempting to replace the memory heated seat/
mirror module.
For complete circuit wiring diagrams, refer to Wir-
ing.
LH
scan tool
scan tool