Heated Seats (KA1)

Heated Seats Description and Operation (KA1)

Description

The driver and passenger heated seats have 2 heat zone operating modes with 3 heat level modes and will operate only while the engine is running. The heat zones are determined by which of the 2 heated seat buttons are pressed, while the heat level is determined by the number of times they are pressed. Pressing the seat cushion button 1 time will activate the seat back and cushion heater elements in the high mode. Each time the seat cushion button is pressed the seat back and cushion heat level is reduced from high to medium, low, and off. Pressing the heated seat back button 1 time will activate only the seat back heater element in the high mode. Each time the seat back button is pressed the seat back heat level is reduced from high to medium, low, and off. During heated seat operation the heat zone operating mode may be changed without affecting the current heat level mode. During a cold ambient remote start activation the heated seats will turn on.

Cadillac Switches

The heated seat switches are an integrated to the HVAC control head and when a heated seat switch is pressed the active switch signal is sent to the memory seat module as a GMLAN message. The memory seat module determines the heated seat mode based on the switch messages and sends a message to the HVAC control head to display the heated seat indicators as necessary.

Chevrolet and GMC Switches

The heated seat switches are momentary contact switches and are inputs to the driver and passenger door lock/window switches. A ground circuit is connected to the switch assembly through the door lock/window switch, and when a heated seat switch is pressed and released a brief switch signal is supplied to the door lock/window switch. Whenever the door module receives an active heated seat switch input, the active switch signal is sent to the memory seat module as a GMLAN message. The memory seat module determines the heated seat mode based on the switch messages and sends a message to the door lock/window switch to display the heated seat indicators as necessary.

Heated Seat Operation

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 back temperatures rise. The seat modules allow heated seat operation only while the engine is running which is determined by a GMLAN serial data circuit message.

Heated Seat Operation with Remote Vehicle Start

The heated seats will turn ON with a remote start only with cooler outside air temperatures and if the vehicle is equipped with an automatic climate control system.

When the remote start button is pressed and the HVAC control module senses cooler outside air temperatures, it sends a serial data message to the MSM commanding it to activate the heated seats. The heated seats will stay ON for approximately 10 minutes or until the ignition is turned to the ON/RUN position. Once the ignition is turned to the ON/RUN position the heated seats will have to be manually turned ON and OFF.

Load Management

The electrical power management function is designed to monitor the vehicle electrical load and determine when the battery is potentially in a high discharge condition. The heated seat system is one of the vehicle loads that is subject to reduction during a battery discharge condition. For more information on load management refer to Electrical Power Management Description and Operation Description and Operation.