GMC Sierra 2000 Owner's Manual page 386

Long Trip/Highway Scheduled Maintenance
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Vehicles With GVWR Above 10,000 lbs. or Equipped with Diesel Engine
Only: Inspect shields and underhood insulation for damage or looseness.
Adjust or replace as required. This is a Noise Emission Control Service.
Applicable only to vehicles sold in the United States.
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Rotate tires. See "Tire Inspection and Rotation" in the Index for proper
rotation pattern and additional information. (See footnote +.)
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Diesel Engine Only: Check the air intake system installation to assure that
gaskets are properly sealed and that all hose connections, fasteners and other
components are tight. Also check to be sure that the air cleaner housing is
properly seated and the cover fits tightly. Tighten connections and fasteners or
replace damaged parts as necessary. This is a Noise Emission Control Service.
Applicable only to vehicles sold in the United States.
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Diesel Engine Only: If your engine has a thermostatically controlled cooling
fan, inspect hoses and ducts for proper hook
whichever occurs first). Be sure the valve works properly. This is a Noise
Emission Control Service. Applicable only to vehicles sold in the
United States.
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up (or every 12 months,
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