service GMC SIERRA DENALI 2015 Service Manual

Black plate (41,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
Driving and Operating 9-41turned on, and one will stay on.
If the lights display momentarily
when the ignition is in ON/RUN, but
none stay on, the knob may have
been turned while the vehicle was
off. To see the indicator, turn the
knob to another position so that it
matches the actual transfer case
setting. If no lights display, take the
vehicle to your dealer for service.
An indicator light flashes while
shifting and until the shift is
complete.
If the transfer case cannot complete
a requested shift, it will return to the
last chosen setting. Turn the control
back to the previous setting to see
the indicator light.
{ Caution
Shifting the transmission into gear
before the requested mode
indicator light has stopped
flashing could damage the
transfer case. The settings are:
N (Neutral): Shift the transfer case
to N (Neutral) only when towing the
vehicle. See Recreational Vehicle
Towing on page 10-91 or Towing the
Vehicle on page 10-91 .
2
m (Two-Wheel Drive High): Use
for driving on most streets and
highways. The front axle is not
engaged. This setting provides the
best fuel economy.
4
n (Four-Wheel Drive Low): This
setting engages the front axle and
delivers extra torque. Choose 4
n if
driving off-road in deep sand, deep
mud, or deep snow, and while
climbing or descending steep hills.
When engaged, keep vehicle speed
below 72 km/h (45 mph).
Shifting into 4
n will turn Traction
Control and StabiliTrak off. See
Traction Control/Electronic Stability
Control on page 9-49 . 4
m (Four-Wheel Drive High): Use
when extra traction is needed. The
front axle engages and helps when
driving on snowy or icy roads, when
off-roading, or when plowing snow.
The vehicle can be shifted from 2
mto 4
m while the vehicle is moving.
Shifting Into 4
m Turn the knob to 4
m at any speed
up to 121 km/h (75 mph), except
from 4
n . The indicator light will flash
while shifting and will remain on the
selected setting.
Shifting Into 2
m Turn the knob to 2
m at any speed,
except when shifting from 4
n .

Black plate (43,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
Driving and Operating 9-438. Turn the engine off, and the
ignition to ACC/ACCESSORY.
9. Place the transmission shift
lever in P (Park).
10. See Recreational Vehicle
Towing on page 10-91 .
11. Turn the ignition to LOCK/OFF.
Shifting Out of N (Neutral)
To shift out of N (Neutral):
1. Set the parking brake and apply
the brake pedal.
2. Turn the ignition to ON/RUN with
the engine off.
3. Shift the transmission to
N (Neutral).
4. Turn the transfer case knob to
2
m .
After the transfer case has
shifted out of N (Neutral), the
N (Neutral) light will go out.
5. Release the parking brake. { CautionShifting the transmission into gear
before the requested mode
indicator light has stopped
flashing could damage the
transfer case.
6. Start the engine and shift the
transmission to the desired gear.
Automatic Transfer Case Use the transfer case knob next to
the steering wheel to shift into and
out of four-wheel drive.
Indicator lights display which setting
the transfer case is in. N (Neutral) is
indicated on the face of the knob.
The indicator lights will display
briefly when the ignition is turned on
and one will stay on. If the lights
display momentarily when the
ignition is in ON/RUN, but none stay
on, the knob may have been turned
while the vehicle was off. To see the
indicator, turn the knob to another
position so that it matches the
actual transfer case setting. If no
lights display, take the vehicle to
your dealer for service. An indicator
light flashes while shifting the
transfer case and remains
illuminated when the shift is
complete.
If the transfer case cannot make a
requested shift, it will return to the
last chosen setting. Turn the knob
back to the previous transfer case
setting to see the indicator.

Black plate (61,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
Driving and Operating 9-61Selecting the Alert Timing
The FCA control is on the steering
wheel. Press
[ to set the FCA
timing to Far, Medium, Near, or Off.
The first button press shows the
current setting on the DIC.
Additional button presses will
change this setting. The chosen
setting will remain until it is changed
and will affect the timing of both the
Collision Alert and the Tailgating
Alert features. The timing of both
alerts will vary based on vehicle
speed. The faster the vehicle speed,
the farther away the alert will occur. Consider traffic and weather
conditions when selecting the alert
timing. The range of selectable alert
timing may not be appropriate for all
drivers and driving conditions.
Unnecessary Alerts FCA may provide unnecessary
alerts for turning vehicles, vehicles
in other lanes, objects that are not
vehicles, or shadows. These alerts
are normal operation and the
vehicle does not need service.
Cleaning the System If the FCA system does not seem to
operate properly, cleaning the
outside of the windshield in front of
the rearview mirror, and cleaning the
front of the vehicle where radar
sensors are located, may correct
the issue. Lane Departure
Warning (LDW) If equipped, LDW may help avoid
crashes due to unintentional lane
departures. It may provide an alert if
the vehicle is crossing a lane
marking without using a turn signal
in that direction. LDW uses a
camera sensor to detect the lane
markings at speeds of 56 km/h
(35 mph) or greater.
{ WarningThe LDW system does not steer
the vehicle. The LDW system
may not: .
Provide enough time to avoid
a crash. .
Detect lane markings under
poor weather or visibility
conditions. This can occur if
the windshield or headlamps
are blocked by dirt, snow,
or ice; if they are not in
(Continued)

Black plate (62,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
9-62 Driving and Operating Warning (Continued) proper condition; or if the sun
shines directly into the
camera. .
Detect road edges. .
Detect lanes on winding or
hilly roads.
If LDW only detects lane
markings on one side of the road,
it will only warn you when
departing the lane on the side
where it has detected a lane
marking. Always keep your
attention on the road and
maintain proper vehicle position
within the lane, or vehicle
damage, injury, or death could
occur. Always keep the
windshield, headlamps, and
camera sensors clean and in
good repair. Do not use LDW in
bad weather conditions. How the System Works The LDW camera sensor is on the
windshield ahead of the rearview
mirror.
To turn LDW on and off, press
@ on
the center stack. The control
indicator will light when LDW is on.
When LDW is on,
@ is green if
LDW is available to warn of a lane
departure. If the vehicle crosses a
detected lane marking without using
the turn signal in that direction,
@changes to amber and flashes.
Additionally, there will be three
beeps, or the driver seat will pulse
three times on the right or left,
depending on the lane departure
direction. When the System Does Not
Seem to Work Properly The system may not detect lanes as
well when there are: .
Close vehicles ahead. .
Sudden lighting changes, such
as when driving through tunnels. .
Banked roads.
If the LDW system is not functioning
properly when lane markings are
clearly visible, cleaning the
windshield may help.
LDW alerts may occur due to tar
marks, shadows, cracks in the road,
temporary or construction lane
markings, or other road
imperfections. This is normal system
operation; the vehicle does not need
service. Turn LDW off if these
conditions continue.

Black plate (63,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
Driving and Operating 9-63
Fuel For diesel engine vehicles, see
“ Fuel for Diesel Engines ” in the
Duramax diesel supplement.
Use of the recommended fuel is an
important part of the proper
maintenance of this vehicle. When
driving in the U.S. and Canada, to
help keep the engine clean and
maintain optimum vehicle
performance, we recommend using
TOP TIER Detergent Gasolines.
See www.toptiergas.com for a list of
TOP TIER Detergent Gasolines. If the vehicle has a yellow fuel cap,
E85 or FlexFuel can be used in the
vehicle. See E85 or FlexFuel on
page 9-65 .
For all vehicles except those with
the 6.2L V8 engine, use regular
unleaded gasoline meeting ASTM
specification D4814 with a posted
octane rating of 87 or higher. Do not
use gasoline with an octane rating
below 87, as it may cause engine
damage and will lower fuel
economy.
If the vehicle has the 6.2L V8 engine
(VIN Code J), use premium
unleaded gasoline meeting ASTM
specification D4814 with a posted
octane rating of 91 or higher.
Regular unleaded gasoline rated at
87 octane or higher can be used,
but acceleration and fuel economy
will be reduced, and an audible
knocking noise may be heard. If this
occurs, use a gasoline rated at
91 octane or higher as soon as
possible. Otherwise, the engine
could be damaged. If heavy knocking is heard when using
gasoline with a 91 octane rating or
higher, the engine needs service.
Use of Seasonal Fuels
Use summer and winter fuels in the
appropriate season. The fuels
industry automatically modifies the
fuel for the appropriate season.
If fuel is left in the vehicle tank for
long periods of time, driving or
starting could be affected. Drive the
vehicle until the fuel is at one-half
tank or less, then refuel with the
current seasonal fuel.
Prohibited Fuels
Gasolines containing oxygenates
such as ethers and ethanol, as well
as reformulated gasolines, are
available in some cities. If these
gasolines comply with the
previously described specification,
then they are acceptable to use.
However, E85 (85% ethanol) and
other fuels containing more than
15% ethanol must be used only in
FlexFuel vehicles.

Black plate (64,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
9-64 Driving and Operating
{ CautionDo not use fuel containing
methanol. It can corrode metal
parts in the fuel system and also
damage plastic and rubber parts.
That damage would not be
covered under the vehicle
warranty.
Some gasolines, mainly high octane
racing gasolines, can contain an
octane-enhancing additive called
methylcyclopentadienyl manganese
tricarbonyl (MMT). Do not use
gasolines and/or fuel additives with
MMT as they can reduce spark plug
life and affect emission control
system performance. The
malfunction indicator lamp may turn
on. If this occurs, see your dealer
for service. California Fuel
Requirements If the vehicle is certified to meet
California Emissions Standards, it is
designed to operate on fuels that
meet California specifications. See
the underhood emission control
label. If this fuel is not available in
states adopting California Emissions
Standards, the vehicle will operate
satisfactorily on fuels meeting
federal specifications, but emission
control system performance might
be affected. The malfunction
indicator lamp could turn on and the
vehicle may not pass a smog-check
test. See Malfunction Indicator
Lamp on page 5-18 . If this occurs,
return to your authorized dealer for
diagnosis. If it is determined that the
condition is caused by the type of
fuel used, repairs may not be
covered by the vehicle warranty. Fuels in Foreign
Countries If planning to drive in countries
outside the U.S. or Canada, the
proper fuel might be hard to find.
Check regional auto club or fuel
retail brand websites for availability
in the country where driving. Never
use leaded gasoline, fuel containing
methanol, manganese, or any other
fuel not recommended. Costly
repairs caused by use of improper
fuel would not be covered by the
vehicle warranty.
Fuel Additives To keep fuel systems clean, TOP
TIER Detergent Gasoline is
recommended. See Fuel on
page 9-63 .
If TOP TIER Detergent Gasoline is
not available, one bottle of Fuel
System Treatment PLUS added to
the fuel tank at every engine oil
change can help. Fuel System
Treatment PLUS is the only

Black plate (71,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
Driving and Operating 9-717. Stop and have someone pick up
and store the chocks.
Maintenance when Trailer
Towing The vehicle needs service more
often when pulling a trailer. See
Maintenance Schedule on
page 11-3 . Things that are
especially important in trailer
operation are automatic
transmission fluid, engine oil, axle
lubricant, belts, cooling system, and
brake system. It is a good idea to
inspect these before and during
the trip.
Check periodically to see that all
hitch nuts and bolts are tight.
Trailer Towing If the vehicle has a diesel engine,
see the Duramax diesel
supplement.
If the vehicle is bi-fuel, see the
bi-fuel supplement. Do not tow a trailer during break-in.
See New Vehicle Break-In on
page 9-23 for more information.
{ WarningThe driver can lose control when
pulling a trailer if the correct
equipment is not used or the
vehicle is not driven properly. For
example, if the trailer is too
heavy, the brakes may not work
well or even at all. The driver and
passengers could be seriously
injured. The vehicle may also be
damaged; the resulting repairs
would not be covered by the
vehicle warranty. Pull a trailer
only if all the steps in this section
have been followed. Ask your
dealer for advice and information
about towing a trailer with the
vehicle. { CautionPulling a trailer improperly can
damage the vehicle and result in
costly repairs not covered by the
vehicle warranty. To pull a trailer
correctly, follow the advice in this
section and see your dealer for
important information about
towing a trailer with the vehicle.
See Vehicle Load Limits on
page 9-15 for more information
about the vehicle's maximum load
capacity.
To identify the trailering capacity of
the vehicle, read the information in
“ Weight of the Trailer ” later in this
section.

Black plate (82,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
9-82 Driving and Operating If the vehicle is equipped with the
heavy-duty trailering option, see
“ Heavy-Duty Trailer Wiring Harness
Package ” earlier in this section.
When the camper-wiring harness is
ordered without the heavy-duty
trailering package, a seven-wire
harness with a seven-pin connector
is at the rear of the vehicle and is
tied to the vehicle's frame.
Electric Brake Control Wiring
Provisions These wiring provisions are
included with the vehicle as part of
the trailer wiring package. These
provisions are for an electric brake
controller.
The harness should be installed by
your dealer or a qualified service
center. Tow/Haul Mode
Pressing this button at the end of
the shift lever turns on and off the
Tow/Haul Mode.
This indicator light on the instrument
cluster comes on when the Tow/
Haul Mode is on. Tow/Haul is a feature that assists
when pulling a heavy trailer or a
large or heavy load. See Tow/Haul
Mode on page 9-39 .
Tow/Haul is designed to be most
effective when the vehicle and
trailer combined weight is at least
75% of the vehicle's Gross
Combined Weight Rating (GCWR).
See “ Weight of the Trailer ” under
Trailer Towing on page 9-71 . Tow/
Haul is most useful under the
following driving conditions: .
When pulling a heavy trailer or a
large or heavy load through
rolling terrain. .
When pulling a heavy trailer or a
large or heavy load in
stop-and-go traffic. .
When pulling a heavy trailer or a
large or heavy load in busy
parking lots where improved low
speed control of the vehicle is
desired.

Black plate (85,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
Driving and Operating 9-85.
A trailer without electric brakes
is connected (no DIC message
will display). .
A trailer with electric brakes has
become disconnected (a
CHECK TRAILER WIRING
message will also display on
the DIC). .
There is a fault present in the
wiring to the trailer brakes (a
CHECK TRAILER WIRING
message will also display on
the DIC). .
The ITBC system is not working
due to a fault (a SERVICE
TRAILER BRAKE SYSTEM
message will also display in
the DIC).
Manual Trailer Brake Apply
The Manual Trailer Brake Apply
Lever is used to apply the trailer ’ s
electric brakes independent of the
vehicle ’ s brakes. Sliding the lever to
the left will apply only the trailer
brakes. Use this lever to adjust
Trailer Gain to properly adjust the
power output to the trailer brakes. The trailer's and the vehicle's brake
lamps will come on when either
vehicle brakes or manual trailer
brakes are applied.
Trailer Gain Adjustment Procedure
Trailer Gain should be set for a
specific trailering condition and must
be adjusted anytime vehicle loading,
trailer loading, or road surface
conditions change.
{ WarningTrailer brakes that are
over-gained or under-gained may
not stop the vehicle and the trailer
as intended and can result in a
crash. Always follow the
instructions to set the Trailer Gain
for the proper trailer stopping
performance. Use the following to adjust Trailer
Gain for each towing condition:
1. Drive the vehicle with the trailer
attached on a level road surface
representative of the towing
condition and free of traffic at
about 32 to 40 km/h (20 to
25 mph) and fully apply the
Manual Trailer Brake Apply
Lever.
Adjusting Trailer Gain at speeds
lower than 32 to 40 km/h (20 to
25 mph) may result in an
incorrect gain setting.
2. Adjust the Trailer Gain, using the
Trailer Gain Adjustment Buttons,
to just below the point of trailer
wheel lock-up, indicated by
trailer wheel squeal or tire
smoke when a trailer wheel
locks.
Trailer wheel lock-up may not
occur if towing a heavily loaded
trailer. In this case, adjust the
Trailer Gain to the highest
allowable setting for the towing
condition.

Black plate (86,1)GMC 2015i Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-8431500) - 2015 - crc - 6/20/14
9-86 Driving and Operating 3. Readjust Trailer Gain anytime
vehicle loading, trailer loading,
or road surface conditions
change or if trailer wheel lock-up
is noticed at any time while
towing.
Other ITBC-Related DIC Messages
In addition to displaying TRAILER
GAIN and OUTPUT through the
DIC, trailer connection and ITBC
system status are displayed on
the DIC.
TRAILER CONNECTED: This
message will briefly display when a
trailer with electric brakes is first
connected to the vehicle. This
message will automatically turn off
in about 10 seconds. This message
can be acknowledged before it
automatically turns off. CHECK TRAILER WIRING: This
message will display if: .
The ITBC system first
determines connection to a
trailer with electric brakes and
then the trailer harness becomes
disconnected from the vehicle.
If the disconnect occurs while
the vehicle is stationary, this
message will automatically turn
off in about 30 seconds. This
message will also turn off if it is
acknowledged or if the trailer
harness is reconnected.
If the disconnect occurs while
the vehicle is moving, this
message will continue until the
ignition is turned off. This
message will also turn off if it is
acknowledged or if the trailer
harness is reconnected. .
There is an electrical fault in the
wiring to the trailer brakes. This
message will continue as long
as there is an electrical fault in the trailer wiring. This message
will also turn off if it is
acknowledged.
To determine if the electrical fault is
on the vehicle side or trailer side of
the trailer wiring harness
connection:
1. Disconnect the trailer wiring
harness from the vehicle.
2. Turn the ignition off.
3. Wait 10 seconds, then turn the
ignition back to RUN.
4. If the CHECK TRAILER WIRING
message reappears, the
electrical fault is on the
vehicle side.
If the CHECK TRAILER WIRING
message only reappears when
connecting the trailer wiring
harness to the vehicle, the
electrical fault is on the
trailer side.
SERVICE TRAILER BRAKE
SYSTEM: This message will display
when there is a problem with the
ITBC system. If this message