SRX AWD V6-3.6L (2008)
Seat Heater: Description and Operation
Heated Seats Description and Operation
Heated Seat Components
The heated seats consist of the following components:
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Left heated seat switch
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Right heated seat switch
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Memory seat module
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Left door module
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Right door module
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Left seat cushion heating element
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Left seat back heating element
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Left seat cushion temperature sensor
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Right seat cushion heating element
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Right seat back heating element
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Right seat cushion temperature sensor
Modes of Operation
The heated seat module (MSM) controls heated seat operation for both the driver and passenger seats. There are 2 modes of operation available for
heated seats; both the seat cushion and seat back heat, or seat back only heat. When a heated seat temperature signal request is received, the MSM will
activate both the seat cushion and seat back heating elements. When the heated seat BACK ONLY mode button is pressed once the MSM will deactivate
the seat cushion heating element and leave the seat back heating element ON.
Heated Seat Switch/LED Indicators and System Operation
The left and right heated seats are controlled by separate heated seat switches located in the door panels. Ground is supplied to the heated seat switches
through the switch low reference circuits from their respective door modules. The door modules also control the heated seat switch heat mode and
temperature indicators. The memory seat module (MSM) controls the heated seat operation for both, the left and right heated seats.
The following describes the sequence of operation and how the MSM responds to each of the switch inputs.
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High Temperature-When the heated seat switch is pressed once, ground is applied through the switch contacts and the switch signal circuit to the
door module indicating the high heat request. In response to this signal, the door module applies a low current voltage through the 3 temperature
indicator control circuits illuminating all 3 LEDs indicating the high temperature mode. The module then sends a message via the GMLAN serial
data line to the MSM indicating the heated seat request. The MSM then applies battery voltage through the heating element supply voltage circuit
to the seat cushion and seat back heating elements. At the same time, it supplies a ground through the element low reference circuits to the seat
heating elements.
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Medium Temperature-When the switch is pressed a second time, the MSM sets the temperature level to medium heat. The door module removes
the voltage from the high temperature indicator leaving 2 LEDs illuminated indicating the medium temperature mode.
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Low Temperature-When the switch is pressed a third time, the MSM sets the temperature level to low heat. The door module removes the voltage
from the medium temperature indicator leaving 1 LED illuminated indicating the low temperature mode.
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System OFF State-When the switch is pressed a fourth time, the MSM removes the battery voltage and grounds from the heating elements. The
door module removes the voltage from the low temperature indicator, indicating the system OFF state.
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Back Only Mode-When the heated seat is ON and the BACK ONLY mode button is pressed, ground is applied through the switch contacts and the
heated seat back only mode signal circuit to the door module. In response to this signal, the door module sends a GMLAN message to the MSM
indicating the back only mode request. The MSM then opens the ground path to the seat cushion heater element, leaving the seat back heater
active. The door module turns OFF the seat cushion/back mode indicator, then applies a low current voltage through the heated seat back only
mode indicator control circuit illuminating the back only mode indicator.
Temperature Regulation
The heated seat system is designed to warm the seat cushion and seat back to approximately 42°C (107.6°F) when in the high position, 39.5°C (103°F)
when in the MED position, and 37°C (98.6°F) when in the low position. The memory seat module (MSM) monitors the seat temperature through the
temperature sensor signal circuits and the temperature sensors (thermistor) that are located in the seat cushion and the seat back. The temperature sensors
are variable resistors, their resistance varies as the temperature of the seat changes. When the temperature sensor resistance indicates to the MSM 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 to maintain the desired temperature.
Load Management
The electrical power management function is designed to monitor the vehicle electrical load and determine when the battery is potentially in a high
