Circuit/System Description

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The driver and front passenger heated seats are controlled through the switch inputs of the HVAC control module. When a heated seat switch is pressed a serial data message is sent from the HVAC control module to the memory seat module (MSM) indicating the heated seat request. In response to this message, the MSM applies battery voltage to the heater element supply voltage circuit and ground through pulse width modulation (PWM) low side drive control circuits activating the heated seat. Once the heated seat is activated, the MSM then sends a serial data message back to the HVAC control module to illuminate the appropriate switch indicators. The MSM relies on 4 independent inputs from thermistors located in the seat back and seat cushion of the driver and passenger seats to control seat temperatures. The thermistors are 2-wire temperature sensors supplied with a 5-volt referenced signal circuit and a low reference circuit from the MSM. Resistance through the sensors varies with seat temperature causing the signal circuit voltage levels to decrease as the seat temperatures rise.