GMC 2003 C4C042 Owner's Manual page 355

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Wheel bearing (grease type) service (or every
24 months, whichever occurs first, and whenever
hubs are removed). (23)(46)
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Inspect door hinge pins and bushings and replace
as necessary.
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Steering system service. (13)
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Front and rear suspension service. (14)
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- - -
Spring to axle U bolts and shackle
bolts service. (16)
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Exhaust system service (or every 6 months,
whichever occurs first). (3)(4)(17)
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Wheels and tires service. (15)
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Hydraulic brake service (or every 6 months,
whichever occurs first). (7)(46)
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Parking brake service (or every 6 months, whichever
occurs first). (8)
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Thermostatically controlled engine cooling fan
service. (4)(20)
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Shields and underhood insulation service. (4)(5)(21)
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Rear axle air shift motor service. (11)
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Air intake system service (or every 24 months,
whichever occurs first). (4)(5)(24)
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Evaporative Control System service (if equipped) (or
every 24 months, whichever occurs first). (3)(26)
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Air brake service (or every 6 months, whichever
occurs first). (39)
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Air brake automatic slack adjuster service
(or every 500 hours, whichever occurs first). (40)
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Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours,
whichever occurs first).
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Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first); lubricate
linkage.
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Air brake chamber service (or every 2 months,
whichever occurs first). (41)
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Trailer brake hand control valve service (or every
3 months, or every 900 hours, whichever
occurs first). (42)
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L18/LB7 Engines Only: Clutch pedal free
travel service. (10)
50,000 Miles (80 000 km)
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DURAMAX
and filter (or every 12 months, whichever occurs
first). (2)(3)
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Inspect air compressor discharge port (or every
6 months or every 1,800 hours, whichever
[
occurs first).
Diesel Only: Change engine oil
7-9