Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

332 Chapter Fifteen
Figure 15-30.
Heated seat circuit. (GM Service and Parts Operations)
(LRDM), and right rear door module (RRDM) are
also involved in the operation of the heated seats.
The system is functional only with the ignition
switch in the ON position.
Power and Grounds
Battery positive voltage is supplied to the front
and rear heated seat module through the ignition
3 voltage circuit and the IGN 3 fuse located in the
rear fuse block. This voltage is used to power up
the module. Battery positive voltage is also supplied
at all times to all four heated seat modules
from the fuses located in the rear fuse block.
The modules to apply voltage to the seat heating
elements use this battery voltage. The left and
right front heated seat modules are grounded
through the module ground circuit and G302. The
left and right rear heated seat modules are
grounded through the module ground circuit and
G301. The left and right front heated seat
switches are grounded through the switch ground
circuit and G200. The left and right rear heated
seat switches are grounded through the switch
ground circuit provided by the associated door
module.
Temperature Regulation
The heated seat system is designed to warm the
seat cushion and seat back to approximately 42C
(107.6F) when in the high position, and 37C
(98.6F) when in the low position. The heated seat
module monitors the seat temperature through the
temperature sensor signal circuit and the temperature
sensor (thermistor) that is located in the seat
cushion. The temperature sensor is a variable
resistor: its resistance changes as the temperature
of the seat changes. When the temperature sensor
resistance indicates to the heated seat module that
the seat has reached the desired temperature, the
module opens the ground path of the seat heating
elements through the heated seat element control
circuit. The module will then cycle the element
control circuit open and closed in order maintain
the desired temperature.
Front Heated Seat Operation
When the heated seat switch is first pressed, the
heated seat high/low signal circuit of the heated
seat module is momentarily grounded through
the HI/LO switch contacts, indicating a high heat