Hummer 2006 H2 - Manual (Page 132)

If your vehicle has the OnStar and navigation system, it
will have a crossrail stop tab placed in the siderail in
the location labeled OnSTAR STOP. This tab prevents
you from moving the crossrails and cargo too close
to the OnStar antenna, which could cause the system to
function improperly or not at all.
Vehicles with the off-road lamps will have additional
stop tabs placed in the siderails to prevent you
from moving the lamps too far rearward, causing them
to shine into the optional sunroof opening.
Crossrail Channels
Notice: If you drive your vehicle through an
automatic car wash that does not have enough
clearance for any roof-mounted accessories (such
as off-road lamps or a roof basket) on your vehicle,
you can damage your vehicle. To avoid damaging
your vehicle in a car wash, remove any
roof-mounted accessories if you can, and do not
use an automatic car wash while roof-mounted
accessories are on your vehicle. See Washing Your
Vehicle on page 5-109 for more information.
The crossrails have built in channels to allow you to
attach other items designed for this system, such
as basket luggage carriers, bike racks, ski racks, etc.
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