Factory Installed Heated Seat System Operation

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The driver and passenger 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 lock/window switches. The door lock/window switches also control the heated seat switch heat mode and temperature indicators. The memory seat module (MSM) controls the heated seat operation for both front 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 lock/window switch indicating the high heat request. In response to this signal, the door lock/window switch applies a low current voltage through the 3 temperature indicator control circuits illuminating all 3 LEDs indicating the high temperature mode. The switch 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.
Medium Temperature-When the switch is pressed a second time, the MSM sets the temperature level to medium heat. The door lock/window switch 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 lock/window switch 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 lock/window switch 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 lock/window switch. In response to this signal, the door lock/window switch 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 lock/window switch 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.