GMC T-Series 2007 Owner's Manual page 318

Engine Cooling System Service
Inspect the hoses and have them replaced if they
are cracked, swollen, or deteriorated. Inspect all
pipes, fittings, and clamps; replace as needed.
Clean the outside of the radiator and air
conditioning condenser. To help ensure proper
operation, a pressure test of the cooling system and
pressure cap is recommended at least once a year.
Exhaust System Inspection
Be alert for any changes in the sound of the
exhaust system or any smell of fumes. These
are signs the system may be leaking. Have
it checked and/or repaired at once. See Engine
Exhaust on page 86 and Running the Engine
While Parked on page 92.
Check to be sure that mud or dirt is not caked
on the exhaust system, especially in the area of
the diesel particulate filter and tailpipe. Clean
the area as needed. See Diesel Particulate Filter
on page 87.
At high mileages, the DPF becomes loaded with
ash. This is normal. When the amount of ash
loading is high, see your dealer/retailer for DPF
cleaning or replacement.
318
Windshield Wipers and Washers Check
Check operation and condition of the wiper
blades. Check the flow of the washer spray.
Defroster Check
Move the control to the defrost symbol and the fan
to HI or the high symbol. Then check the airflow
from the ducts at the inside base of the windshield.
Mirrors and Sun Visors Check
Check that friction joints hold mirrors and sun
visors in place.
Seat Adjuster Check
When adjusting a manual seat, be sure seat
adjusters latch by attempting to move the seat
after latching.