Here's a little reading material for you - I'll keep looking for more info:
Heated Seats Circuit Description
Battery positive voltage (B+) is applied at all times to the left heated seat module from the rear junction block HTDST L fuse through CKT 1040 (ORN).
Battery positive voltage (B+) is applied at all times to the right heated seat module from the rear junction block HTDST R fuse through CKT 1440 (ORN).
Each module receives an ignition input from the IP junction block IGN SEN fuse through CKT 241 (BRN). The heated seat modules both receive ground from G201 through CKT 450 (BLK). The system operates only when the ignition is in the RUN position.
When you press the heated seat switch, the heated seat module heated seat switch input terminal momentarily grounds through 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. The heated seat module maintains a pre-determined temperature. The heated seat module will set the heated seat temperature to high under the following conditions:
The heated seat is off.
The heated seat switch is pressed once.
When the heated seat switch is pressed again, the heated seat temperature sets to low. After you press the heated seat switch 3 times, the heated seat module stops applying battery positive voltage (B+) to the heating elements. The module also turns off the heated seats whenever the ignition switch is in the OFF position.
Temperature Regulation
GM engineers designed the heated seat system in order to warm the seat cushion and the seat back. In the low position, the seat heats to approximately 37°C (98.6°F). In the high position, the seat heats to approximately 44°C (111.2°F).
The temperature sensor in the seat cushion is a variable resistor called a thermistor. The thermistor regulates the temperature of the seat. The resistance of the sensor varies 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. The module opens the contacts in order to remove battery positive voltage (B+) from the heating elements under the following conditions:
The heated seat switch is in the LOW position.
The heating element temperature reaches 37°C (98.6°F).
The module also opens the contacts in order to remove battery positive voltage (B+) from the heating elements under the following conditions:
The heated seat switch is in the HIGH position.
The heating element temperature reaches 44°C (111.2°F).
The heated seat module cycles on and off in order to maintain the desired temperature. The system remains active until one of the following conditions occurs:
The system is turned off.
The ignition switch is turned to the OFF position.
LED Indicators
When the heated seat is in one of the following positions, the heated seat module supplies battery positive voltage (B+) to the appropriate LED on the heated seat switch in order to illuminate the indicator:
LOW
HIGH
The indicator receives ground from G201 through CKT 450 (BLK).
Load Management
The load management feature controls the amount of power consumed in the vehicle under heavy power load demands. If the vehicle demands high power for over 2 minutes, the body control module (SBM) cycles the power output to the heated seats at approximately 50% of normal capacity. The load management feature occurs under the following conditions:
The blower is set to the HIGH position.
The headlamps are in the ON position.
The rear window defroster is in the ON position.
One of the heated seats is in the ON position.
Due to the load management function, customers may complain that the heated seats do not warm up quickly or warm at a lower temperature than normal. Deactivate one of the above systems in order to deactivate the load management function.
