1999 GMC Sonoma Owner's Manual - Page 9

yellowblue Manual Lumbar Support (If Equipped) If you have this feature, there will be a knob on the outside of the driver and passenger bucket seats. Reclining Seatbacks (Bucket Seats or 60/40 Bench) To adjust the front seatback, lift the lever on the outer side of the seat. Turn the knob toward the front of the vehicle to increase lumbar support and toward the rear of the vehicle to decrease lumbar support. Release the lever to lock the seatback where you want it. Pull up on the lever and the seat will go to an upright position. 1-3