GMC 1996 Sierra Owner's Manual page 315

Underbody Maintenance
Chemicals used for ice and snow removal and dust
control can collect
on the underbody, If these are
not removed, accelerated corrosion (rust) can occur
on the underbody parts such as fuel lines, frame,
floor pan and exhaust system even though they have
corrosion protection.
At least every spring, flush these materials from the
underbody with plain water. Clean any areas where mud
and other debris can collect. Dirt packed in closed areas
of the frame should be loosened before being flushed.
Your dealer or an underbody vehicle washing system
can do this for you.
Chemical Paint Spotting
Some weather and atmospheric conditions can create a
chemical fallout. Airborne pollutants can f d l upon and
attack painted surfxes on your vehicle. This damage
can
take two forms: blotchy, ringlet-shaped discolorations, and
small irregular dark spots etched into the paint surface.
Although no defect in the paint job causes this, GM
will repair, at no charge to the owner, the surfaces of
new vehicles damaged by this fallout condition within
12 months or 12,000 miles (20 000 km) of purchase,
whichever occurs first.
This applies only to materials manufactured and sold by
General Motors. Bodies, body conversions or equipment
not made or sold by General Motors are not covered.
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