Heated Seat Switch/LED Indicators and System Operation with A45

The left and right heated seats are controlled by separate heated seat switches. Ground for both heated seat switches is supplied at G302. The driver and passenger door modules 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.

• 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 serial data message to the MSM indicating the heated seat request. The MSM then applies battery voltage through the heating element supply voltage circuit and ground through the element low reference circuits seat cushion and seat back heating elements.
• 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.
• 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.
• 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.
• 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 serial data message to the MSM indicating the back only mode request. The MSM then opens the ground path to the seat cushion heater element, leaving just 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.