Heated Seats

Battery positive voltage (B+) is applied at all times to the LH heated seat module from the rear junction block HTDST L Fuse via CKT 1040 (ORN) and the RH heated seat module from the rear junction block HTDST R Fuse via CKT 1440 (ORN). Each module receives an ignition input from the I/P Junction block IGN SEN Fuse via CKT 241 (BRN). The heated seat modules both receive ground from G201 via CKT 450 (BUC). The system will only operate when the ignition switch is in RUN.

When the heated seat switch is pressed, the heated seat module heated seat switch input terminal is momentarily grounded via CKT 450 (BLK). The heated seat module then applies battery positive voltage (B+) to the heated seats. The heated seat module monitors the seat surface temperature through a thermistor and maintains a pre-determined temperature. When the heated seat is off and the seat heat switch is pressed once, the heated seat module will set the heated seat temperature to high. When pressed again, the heated seat temperature is then set to low. After the third press of the seat heat switch, the heated seat module stops applying battery positive voltage (B+) to the heating elements. The module will also turn off the heated seats whenever the ignition switch has been turned off.

Temperature Regulation
The heated seat system is designed to warm the seat cushion and backrest to approximately 37°C (98.6°F) when in the low position and 44°C (111.2°F) when in the high position.

To regulate the temperature of the seats, a temperature sensor is installed in the seat cushion, called the thermistor. The sensor is a variable resistor (its resistance changes as the temperature of the seat cushion changes). The heated seat module monitors the sensor resistance at the sensor input on connector C2 cavity C. When the heated seat switch is in the low position and the heating element temperature reaches 37°C (98.6°F), the module opens its contacts removing battery positive voltage (B+) from the heating elements.

If the heated seat switch is in the high position, battery positive voltage (B+) is removed when the heating elements temperature reaches 44°C (111.2°F). The heated seat module will cycle on and off to maintain the desired temperature. The system will remain active until the system or the ignition switch is turned off.

LED Indicators
When the heated seats is in either the low or high, the heated seat module supplies battery positive voltage (B+) to the appropriate LED on the heated seat switch to illuminate the indicator. The indicator is grounded through CKT 450 (BLK) at ground G201

Load Management
The load management feature controls the amount of power consumed in the vehicle under heavy power load demands. If the vehicle sees high power demands for over two minutes, the Body Control Module (SBM) will cycle the power output to the heated seats at approximately 50% of normal capacity.

This will occur when all of the following are active:
^ blower set to high.
^ headlamps.
^ rear window defroster.
^ either heated seat.

As a result, customers may complain that the heated seats do not warm up as fast or are warming at lower temperature than normal. To deactivate load management, one of the above conditions must be deactivated.