Chevrolet 2000 Express Van Owner's Manual page 86

Sliding Side Door (Option)
To open the sliding side door from outside, pull the
handle toward the rear of the vehicle. Then, slide the
door open.
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To close the sliding side door from outside, use the
outside door handle to slide the door toward the front of
the vehicle.
When the door slides closed completely, it will be flush
with the side of the body.
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