GMC Sierra Owners Manual
Fixed Mast Antenna
The fixed mast antenna can withstand most car washes without being damaged as long as it is securely attached to the base. If the mast becomes slightly bent, straighten it out by hand. If the mast is badly bent, replace it.
Occasionally check to make sure the antenna is tightened to its base.
If tightening is required, tighten by hand until fully seated plus one quarter turn.