Circuit/System Description

The heated seat system operation is controlled through the switch inputs to the driver and passenger door modules. When a heated seat switch is pressed a GMLAN message is sent to the memory seat module (MSM) indicating the switch is active. The MSM monitors the heated seat switch inputs and determines the appropriate operating mode. When a heated seat function is activated the MSM will send a GMLAN message to the door module to illuminate the appropriate indicators. The memory seat module controls the voltage supply and the ground circuits to the seat heater elements. When a heated seat function is commanded active, the seat module will switch battery voltage to the heater element supply circuits, and ground is provided through pulse width modulation (PWM) low side drive control circuits. During heated seat operation both the seat back and cushion heater elements are supplied battery voltage. The seat module grounds the appropriate control circuits for back only or back and cushion heating modes, and opens or closes the active control circuits as necessary in order to maintain the desired seat temperature. The seat module relies on 4 independent inputs from thermistors located in the seat back and seat cushion of the driver and passenger seats to control heated seat temperatures. The thermistors are 2-wire sensors supplied with a 5-volt referenced signal circuit and a low reference circuit from the seat module. Resistance through the thermistors varies with temperature causing the heated seat sensor signal circuit voltage levels to decrease as the seat temperatures rise.