For 1990-2009 cars

### Heated Seat Components

The driver and passenger heated seats consist of the following components:

• | Left heated seat switch

• | Right heated seat switch

• | HVAC control

• | Heated seat module

• | Left seat cushion heating element

• | Left seat back heating element

• | Left seat cushion temperature sensor

• | Right seat cushion heating element

• | Right seat back heating element

• | Right seat cushion temperature sensor

### Power and Ground

Battery positive voltage is supplied at all times to the heated seat module from the F33UA fuse located in the under-bonnet fuse block. This voltage is used by the module to supply power to the seat heating elements. The module is grounded through the module ground circuit and G307.

### Heated Seat Operation

The driver and passenger heated seats are controlled by a single heated seat module that is located under the driver seat cushion. Both heated seats are controlled by separate heated seat switches that are located in the HVAC control. When a heated seat switch is pressed, the HVAC control sends a message via LIN-Bus to the HVAC control module. The HVAC control module then serves as a gateway to transmit the message to the heated seat module via GMLAN serial data indicating the heated seat command. In response to this signal, the heated seat module then applies battery positive voltage through the element supply voltage circuit to the appropriate seat heating elements. The heated seat module then sends a serial data message back to the HVAC control module to gateway the information to the HVAC control to either illuminate or turn off the appropriate temperature indicator.

### Temperature Regulation

When the ignition is turned to the ON position, the heated seats will initialize in the OFF state. With each activation of the heated seat switch, the heated seat module will cycle the temperature setting in the following manner: HIGH, LOW, and OFF.

The heated seat system is designed in order to warm the seat cushion and seat back to approximately 42°C (107.6°F) when in the high heat position, and 37°C (98.6°F) when in the low heat position. The heated seat module monitors the seat temperature through the temperature sensor signal circuit and the temperature sensor (thermistor) that is located in the seat cushion. The temperature sensor is a variable resistor, it's resistance changes as the temperature of the seat changes. When the temperature sensor resistance indicates to the heated seat module that the seat has reached the desired temperature, the module opens the ground path of the seat heating elements through the heated seat element control circuit. The module will then cycle the element control circuit open and closed in order to maintain the desired temperature.

### 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.