Circuit/System Description

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The driver and front passenger heated seats are controlled by separate heated seat switches located on the door panels. When a heated seat switch is pressed, ground is momentarily applied through the switch contacts and the switch signal circuit to the door control module. In response to this signal, the door module sends a serial message to the memory seat module (MSM) or heated seat module (HSM) indicating the heat seat request. The module then applied battery voltage to the seat cushion and seat back heater elements through a common voltage supply circuit. Each individual heater element is grounded by the module through separate low side drive control circuits. The heater element control circuits are pulse width modulated (PWM) to ground by the module in order to control the seat temperatures by regulating the current flow through the heater elements. The MSM/HSM relies on 4 independent inputs from temperature sensors (thermistors) located in the seat back and seat cushion of the driver and passenger seats. The temperature sensor resistance varies based on the temperature of the heating element causing the signal circuit voltage to change. Once the seat reaches the switch set temperature, the MSM/HSM will then cycle the control circuits of the heating elements ON and OFF in order to maintain the desired seat temperature based on the feedback voltage from the sensors. The MSM/HSM then monitors the current flow through the heating elements and the of rate change of the temperature sensor to verify correct heated seat operation.