2003 GMC Sonoma Owner's Manual - Page 12

Power Lumbar If your vehicle has this feature, there will be a control located on the outboard side of the front seat(s). Heated Seats If your vehicle has this feature, the controls are located on the outboard side of the front seats. Press and hold the front of the control until you have the desired lumbar support. To decrease lumbar support, press and hold the rear of the control. This feature will quickly heat the lower cushion and lower back of the driver's and front passenger's seats for added comfort. Press the lower part of the switch to turn the heater on low. Press the upper part of the switch to turn the heater on high. Put the switch in the center position to turn the heater off. The passenger's safety belt must be engaged for the heated seat feature to work on the passenger's seat. 1 -5