GM Service Manual Online
For 1990-2009 cars only

When the heated seat switch is in the LO position, and the ignition switch is in the RUN position, the heated seat control module LO input terminal is momentarily grounded. The seat control module then turns ON the heater in the seat. The heated seat control module monitors the seat surface temperature through a thermistor located in the center seat bottom. The heated seat control module will maintain the seat surface temperature at 37.5°C (98.5°F) when LO is selected. The HI position is similar to the LO operation except that the temperature increases by 5 degrees. When the switch is in the OFF position, the heated control module's OFF input is grounded momentarily. The module will react by turning the voltage to the seat heaters. The module will also turn OFF the heated seats whenever the ignition switch has been turned to the OFF postion. The passenger heated switch will not operate unless the seat belt is connected. The safety mechanism will insure that the seat will never be left in the ON position.