Relay Usage
ECU/PTO*Engine Control Unit/Power Take-Off
*Diesel 7.8 DURAMAX
®
BRK LAMPC4/C5 Brake Lamps,
C6/C7/C8 Tractor/Trailer Wiring
DRL Daytime Running Lamps
IGN-4 Ignition
CHMSL Center High Mounted Stoplamp
MRK LTS Sidemarker and Clearance Lamps
HTD/MIRR Heated Mirrors
HTR Diesel Heated Fuel
RT TRN TRLR Passenger Side Trailer Turn Signal
Blank Not Used
LT TRN TRLR Driver Side Trailer Turn Signal
Blank Not Used
Blank Not Used
Blank Not Used
Underhood Fuse Block
When a circuit goes out, the problem could be in either
the primary or secondary underhood fuse blocks.
These blocks use blade-type fuses.
Both underhood fuse blocks are located in the engine
compartment, on the passenger side of the vehicle.To access the fuse blocks, gently squeeze both sides of
the cover to unlatch the tabs at the top. Then, unsnap
both attachments at the bottom and remove the cover.
Notice:Spilling liquid on any electrical components
on your vehicle may damage it. Always keep the
covers on any electrical component.
Be sure to replace fuses with fuses of the same rating.
Do not use fuses of higher amperage than those
indicated on the fuse block.
Primary Underhood Fuse Block
5-106
Fuse Usage
RR DEFOG Rear Defogger
ENG 1 Engine 1
ENG 3 Engine 3 (L18/LF6/LF8)
PCM-B Powertrain Control Module
TCM Transmissions (LF8)
ENG 4 Engine 4 (LMM/LF6/LF8)
ENG 2 Engine 2 (L18/LMM)
HTD FUEL Heated Fuel (LMM)
BLANK Not Used
BLANK Not Used
NOTE 3 Fan Relay (LMM), Emissions (L18)
A/C COMP Air Conditioning Compressor
ABS 1 Antilock Brake System 1
ABS 2 Antilock Brake System 2
ABS 3 Antilock Brake System 3
ENGINE Engine
E/A PUMP Electronic/Automatic Pump
HORN HornFuse Usage
NOTE 2Fuel (L18/LMM), Electronic Control
Module (LF6)
NOTE 4 Electronic Control Module (LF6)
STUD A Spare
STUD B Spare
Relay Usage
NOTE 1 LMM/L18 Fuel Pump Relay
IGN B RELAY Ignition Relay
STARTER
RELAYStarter Relay
HORN RELAY Horn Relay
IGN A RELAY Ignition Relay
PTO/ECU*
RELAYPower Take-Off/Engine Control Unit
(*Diesel 7.8L LF8)
REVERSE
RELAYReverse Relay
FAN RELAY Fan Relay (LMM)
5-107
Scheduled Maintenance
The services shown in this schedule up to 100,000 miles
(166 000 km) should be repeated after 100,000 miles
(166 000 km) at the same intervals for the life of
this vehicle. The services shown after 100,000 miles
(166 000 km) should be repeated at the same miles (km)
after those intervals for the life of this vehicle.
Gasoline engine vehicles and some DURAMAX
®diesel
and Isuzu diesel engine vehicles have a computer
that lets you know when to change the engine oil. This
is not based on mileage, but on engine operation and
engine temperature. When the computer has calculated
that the oil needs changing, the Engine Oil Life System
will indicate that a change is necessary. SeeEngine Oil
Life System (Gasoline Engine) on page 5-36orEngine
Oil Life System (DURAMAX
®/Isuzu Diesel Engines) on
page 5-37orEngine Oil Life System (Caterpillar®Diesel
Engine) on page 5-39.
The “Footnotes” at the end of this Maintenance
Schedule further explain maintenance services.
SeeService Publications Ordering Information on
page 7-10.
100 Miles (160 km)
❑Wheel stud nut service.(36)
1,000 Miles (1 600 km)
❑Wheel stud nut service.(36)
❑Rear axle air shift motor service.(10)
7,500 Miles (12 000 km)
❑Gasoline Engine Only: Check engine oil life system.
If engine oil and filter are changed, reset system.
See “Engine Oil (Gasoline Engine)” in the
Index.(2) (8)
❑Check fluid levels (or every 3 months, whichever
occurs first).(1) (5)
❑Chassis lubrication service (or every 6 months,
whichever occurs first).(11)
❑Spring-to-axle U-bolts and shackle bolts service.(15)
❑Wheels and tires service.(14)
❑Hydraulic brake service (or every 6 months,
whichever occurs first).(6) (36)
❑Parking brake service (or every 6 months, whichever
occurs first).(21)
❑Air brake service (or every 6 months, whichever
occurs first).(32)
❑Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first).(33)
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
6-5
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
15,000 Miles (24 000 km)
❑Gasoline Engine Only: Check engine oil life system.
If engine oil and filter are changed, reset system.
See “Engine Oil (Gasoline Engine)” in the
Index.(2) (8)
❑DURAMAX
®/Isuzu Diesel Without Engine Oil Life
System Only: Change engine oil and filter (or every
12 months, or every 750 hours of engine operation,
whichever occurs first).(2) (39)
❑DURAMAX
®/Isuzu Diesel With Engine Oil Life System
Only: Check oil life system. If engine oil and filter are
changed, reset system. See “Engine Oil
(DURAMAX
®/Isuzu Diesel)” in the Index.(2) (9)
❑Chassis lubrication service (or every 6 months,
whichever occurs first).(11)
❑Check fluid levels (or every 3 months, whichever
occurs first).(1) (5)
❑Gasoline Engine: Inspect engine air cleaner filter.
If necessary, replace the filter. If vehicle is driven in
dusty/dirty conditions, inspect filter at every engine oil
change. SeeEngine Air Cleaner/Filter on page 5-39
for more information.❑Diesel Engine: Inspect engine air cleaner filter change
indicator. If necessary, replace the filter. If vehicle is
driven in dusty/dirty conditions, inspect filter change
indicator at every engine oil change. SeeEngine Air
Cleaner/Filter on page 5-39for more information.
❑DURAMAX
®/Isuzu Diesel Only: Replace fuel filter (or
every 750 hours of engine operation, whichever
occurs first).
❑Steering system service.(12)
❑Front and rear suspension service.(13)
❑Spring-to-axle U-bolts and shackle bolts service.(15)
❑Exhaust system service (or every 6 months, whichever
occurs first).(2) (3) (16)
❑Wheels and tires service.(14)
❑Hydraulic brake service (or every 6 months, whichever
occurs first).(6) (36)
❑Parking brake service (or every 6 months, whichever
occurs first).(21)
❑Air brake service (or every 6 months, whichever
occurs first).(32)
❑Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first).(33)
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
6-6
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
❑Air compressor dry element pleated paper air strainer
service (or every 2 months, or every 800 hours,
whichever occurs first).
❑Thermostatically controlled engine cooling fan
service.(3) (19)
❑Shields and underhood insulation service.(3) (4) (20)
❑Gasoline Engine: Air compressor remote mounted air
filter dry element pleated paper air strainer service (or
every 6 months or every 1800 hours, whichever
occurs first).
22,500 Miles (36 000 km)
❑Gasoline Engine Only: Check engine oil life system.
If engine oil and filter are changed, reset system.
See “Engine Oil (Gasoline Engine)” in the
Index.(2) (8)
❑Check fluid levels (or every 3 months, whichever
occurs first).(1) (5)
❑Chassis lubrication service (or every 6 months,
whichever occurs first).(11)
❑Inspect door hinge pins and bushings and replace as
necessary.❑Cooling system service. Clean the cooling system
filter cap with clean water, clean the core, pressure
test the cap and the system for proper pressure
capability, and inspect condition of cooling and heater
hoses and clamps. Replace hoses if cracked,
swollen, or damaged.
❑Wheels and tires service.(14)
❑Hydraulic brake service (or every 6 months,
whichever occurs first).(6) (36)
❑Parking brake service (or every 6 months, whichever
occurs first).(21)
❑Air brake service (or every 6 months, whichever
occurs first).(32)
❑Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first).(33)
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
❑Air brake system valve service (or every 3 months,
or every 900 hours, whichever occurs first).(37)
❑Air intake system service (or every 24 months,
whichever occurs first).(3) (4) (23)
6-7
❑Air brake service (or every 6 months, whichever
occurs first).(32)
❑Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first).(33)
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
❑Air compressor dry element pleated paper air strainer
service (or every 2 months, or every 800 hours,
whichever occurs first).
❑C600, C700, and C800 Gasoline Engines Only:
Engine drive belts service (or every 12 months,
whichever occurs first.)(17)
❑Thermostatically controlled engine cooling fan
service.(3) (19)
❑Shields and underhood insulation service.(3) (4) (20)
❑Gasoline Engine: Air compressor remote mounted
air filter dry element pleated paper air strainer
service (or every 6 months or every 1800 hours,
whichever occurs first).37,500 Miles (60 000 km)
❑Gasoline Engine Only: Check engine oil life system.
If engine oil and filter are changed, reset system.
See “Engine Oil (Gasoline Engine)” in the
Index.(2) (8)
❑Check fluid levels (or every 3 months, whichever
occurs first).(1) (5)
❑Chassis lubrication service (or every 6 months,
whichever occurs first).(11)
❑Wheels and tires service.(14)
❑Hydraulic brake service (or every 6 months,
whichever occurs first).(6) (36)
❑Parking brake service (or every 6 months, whichever
occurs first).(21)
❑Air brake service (or every 6 months, whichever
occurs first).(32)
❑Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first).(33)
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
6-9
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
❑Air brake system valve service (or every 3 months,
or every 900 hours, whichever occurs first).(37)
❑Air compressor dry element pleated paper air strainer
service (or every 2 months, or every 800 hours,
whichever occurs first).
❑Thermostatically controlled engine cooling fan
service.(3) (19)
❑Shields and underhood insulation service.(3) (4) (20)
❑Rear axle air shift motor service.(10)
❑Air intake system service (or every 24 months,
whichever occurs first).(3) (4) (23)
❑Evaporative Control System service, if equipped,
(or every 24 months, whichever occurs
first).(2) (24) †
❑Gasoline Engine: Air compressor remote mounted air
filter dry element pleated paper air strainer service
(or every 6 months or every 1800 hours, whichever
occurs first).48,000 Miles (75 000 km)
❑Lubricate U-joints (or every 6 months, whichever
occurs first).
50,000 Miles (80 000 km)
❑Inspect air compressor discharge port (or every
6 months or every 1,800 hours, whichever
occurs first.)
52,500 Miles (84 000 km)
❑Gasoline Engine Only: Check engine oil life system.
If engine oil and filter are changed, reset system.
See “Engine Oil (Gasoline Engine)” in the
Index.(2) (8)
❑Check fluid levels (or every 3 months, whichever
occurs first).(1) (5)
❑Chassis lubrication service (or every 6 months,
whichever occurs first).(11)
❑Wheels and tires service.(14)
❑DURAMAX
®Diesel Engine Only: Adjust valve lash
(or every 2,625 hours of engine operation, whichever
occurs first).(18)
❑Hydraulic brake service (or every 6 months,
whichever occurs first).(6) (36)
❑Parking brake service (or every 6 months, whichever
occurs first).(21)
6-11
❑Air brake service (or every 6 months, whichever
occurs first).(32)
❑Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first).(33)
❑Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
❑Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first). Lubricate
linkage.
❑Air brake chamber service (or every 2 months,
whichever occurs first).(34)
60,000 Miles (96 000 km)
❑Gasoline Engine Only: Check engine oil life system.
If engine oil and filter are changed, reset system.
See “Engine Oil (Gasoline Engine)” in the
Index.(2) (8)
❑DURAMAX
®/Isuzu Diesel Without Engine Oil Life
System Only: Change engine oil and filter (or
every 12 months, or every 750 hours of engine
operation, whichever occurs first).(2) (39)
❑DURAMAX
®/Isuzu Diesel With Engine Oil Life
System Only: Check oil life system. If engine oil and
filter are changed, reset system. See “Engine Oil
(DURAMAX
®/Isuzu Diesel)” in the Index.(2) (9)
❑Gasoline Engine Only (Vehicles with GVW greater
than 16,000 lbs): Spark plug service.(2) (25)❑Check fluid levels (or every 3 months, whichever
occurs first).(1) (5)
❑Gasoline Engine: Inspect engine air cleaner filter.
If necessary, replace the filter. If vehicle is driven
in dusty/dirty conditions, inspect filter at every engine
oil change. SeeEngine Air Cleaner/Filter on
page 5-39for more information.
❑Diesel Engine: Inspect engine air cleaner filter
change indicator. If necessary, replace the filter.
If vehicle is driven in dusty/dirty conditions, inspect
filter change indicator at every engine oil change. See
Engine Air Cleaner/Filter on page 5-39for more
information.
❑DURAMAX
®/Isuzu Diesel Only: Replace fuel filter
(or every 750 hours of engine operation, whichever
occurs first).
❑Chassis lubrication service (or every 6 months,
whichever occurs first).(11)
❑Replace fuel filter(s) (or every 12 months, whichever
occurs first).(2)
❑Inspect door hinge pins and bushings and replace as
necessary.
❑Check restraint system.(40)
❑Steering system service.(12)
❑Front and rear suspension service.(13)
❑Spring-to-axle U-bolts and shackle bolts service.(15)
6-12