2007 GMC SIERRA CLASSIC brakes

MANUAL MODE (M):This position, is available
on vehicles with the Allison Transmission®.It
lets drivers select the range of gears appropriate
for current driving conditions. If your vehicle
has this feature, see Range Select Mode (Allison
Transmission
®) later in this section.
THIRD (3):This position is also used for normal
driving. However, it reduces vehicle speed
more than DRIVE (D) without using your brakes.
You might choose THIRD (3) instead of DRIVE (D)
when driving on hilly, winding roads, when
towing a trailer, so there is less shifting between
gears and when going down a steep hill.
SECOND (2):This position reduces vehicle speed
even more than THIRD (3) without using your
brakes. You can use SECOND (2) on hills. It can
help control your speed as you go down steep
mountain roads, but then you would also want to
use your brakes off and on.
If you manually select SECOND (2) in an
automatic transmission, the transmission will start
in second gear. You can use this feature for
reducing the speed of the rear wheels when you
are trying to start your vehicle from a stop on
slippery road surfaces.For an Allison Transmission
®, see Low Traction
Mode later in this section.
FIRST (1):For an automatic transmission, this
position reduces vehicle speed even more than
SECOND (2) without using your brakes. You can
use it on very steep hills, or in deep snow or mud. If
the shift lever is put in FIRST (1) while the vehicle is
moving forward, the transmission will not shift into
rst gear until the vehicle is going slowly enough.
For an Allison Transmission
®, This position reduces
vehicle speed, without using your brakes. You can
use it for major/sever downgrades and off-road
driving where the vehicle would otherwise
accelerate due to steepness of grade. When you
shift to FIRST (1) it will provide the lowest gear
appropriate to your current road speed and will
continue to downshift as the vehicle slows,
eventually downshifting to FIRST (1) gear.
Notice:Spinning the tires or holding the
vehicle in one place on a hill using only the
accelerator pedal may damage the
transmission. The repair will not be covered by
your warranty. If you are stuck, do not spin
the tires. When stopping on a hill, use the
brakes to hold the vehicle in place.
144

Low Traction Mode
(Allison Transmission®)
If your vehicle has the DURAMAX®diesel engine
and the Allison Transmission®,ithasaLow
Traction Mode that assists in vehicle acceleration
when road conditions are slippery, such as
with ice or snow. While at a stop, selecting the
second gear range using the Range Selection
system, will allow the Allison Transmission
®to limit
torque to the wheels after it detects wheel slip,
preventing the tires from spinning.
Notice:Spinning the tires or holding the
vehicle in one place on a hill using only the
accelerator pedal may damage the
transmission. The repair will not be covered by
your warranty. If you are stuck, do not spin
the tires. When stopping on a hill, use the
brakes to hold the vehicle in place.
Cold Weather Operation
(Allison Transmission®)
On cold days, approximately 32°F (0°C) or colder,
your automatic transmission is designed to shift
differently. The transmission uses a warm-up mode
shift schedule until the engine reaches normal
operating temperature. While the transmission is
in warm-up mode it is normal for transmission
upshifts to be delayed or held longer. This feature
improves heater performance by giving quicker
vehicle warm-ups.
When temperatures are below−13°F (−25°C), the
transmission will prevent certain operations to
protect against damage. When active the DIC will
display the message “Trans in Warm-up”.
SeeDIC Warnings and Messages on page 270for
more information.
146

Tow/Haul Mode (Allison
Transmission®)
If your vehicle has an Allison Transmission®,it
may have a Tow/Haul mode. Tow/Haul mode
adjusts the transmission shift pattern to reduce
shift cycling, providing increased performance,
vehicle control, and transmission cooling
when towing or hauling heavy loads.The selector button is located on the end of the shift
lever. Turn the Tow/Haul on and off by pressing the
button. When the Tow/Haul is on, a light on the
instrument panel cluster will come on.
SeeTow/Haul Mode Light on page 264for more
information.
Also see “Tow Haul Mode” underTowing a Trailer
on page 429for more information.
Grade Braking and Cruise Grade
Braking (Allison Transmission®)
Grade Braking and Cruise Grade Braking assists
when driving on a downhill grade. It maintains
the vehicle’s speed by automatically using a shift
schedule that uses the engine and the
transmission to slow the vehicle. This reduces
wear on the brakes system and increases control
of the vehicle. The system constantly monitors
the vehicle’s speed, acceleration, engine torque,
and brake pedal usage. It detects when the
truck is on a downhill grade and the driver’s desire
to slow down by pressing the brake.
148

Shift Speeds
{CAUTION:
If you skip a gear when you downshift,
you could lose control of your vehicle.
You could injure yourself or others. Do
not shift down more than one gear at a
time when you downshift.
Do not allow the engine Revolutions Per Minute
(RPM) to overspeed and enter the tachometer red
lines. Engine overspeed occurs when downshifting,
or descending a grade, at too high a vehicle
speed. When going down steep grades, always
select a gear at least one position lower than you
would use on climbing a grade. This will allow
the vehicle’s engine to provide some braking and
help to slow the vehicle as it goes down the
grade. Monitor your vehicle speed, acceleration
and engine RPM while applying the brakes as you
go down the grade to ensure you have complete
control over the vehicle.If your engine speed drops below 600 rpm, or if
the engine is not running smoothly, you should
downshift to the next lower gear. When operating
on slippery surfaces, downshift at lower than
normal vehicle speeds to prevent the tires from
slipping.
In vehicles that have a bench seat, move the
tallest beverage containers to the right cupholder
to provide additional clearance for the shift
lever.
For vehicles that have a center console, the front
cup holder pulls out and turns 180° to provide
additional clearance between tall beverage
containers and the shift lever.
Up-Shift Light
If your vehicle has a
manual transmission,
you may have a shift
light. This light will show
you when to shift to the
next higher gear for best
fuel economy.
152

If torque lock does occur, you may need to have
another vehicle push yours a little uphill to
take some of the pressure from the parking pawl
in the transmission, so you can pull the shift
lever out of PARK (P).
Shifting Out of Park (P)
(Automatic Transmission)
Your vehicle has an automatic transmission shift
lock control system which locks the shift lever
in PARK (P) when the ignition is in the LOCK
position. You have to fully apply your regular
brakes before you can shift from PARK (P) when
the ignition is in RUN. SeeAutomatic Transmission
Operation on page 140and “Torque Lock”
underShifting Out of Park (P) (Automatic
Transmission) on page 172.
If your vehicle has an Allison Transmission
®, the
transmission has a park pawl designed to hold the
higher weight of commercial medium duty
trucks. Therefore, the Allison Transmission
®uses
larger parts than other automatic transmissions.
These larger parts may sometimes make a
clunking noise when the selector lever is movedfrom DRIVE (D) or REVERSE (R) to PARK (P).
This is normal and there is no damage occurring
during these shifts.
If you cannot shift out of PARK (P), ease pressure
on the shift lever and push the shift lever all the
way up into PARK (P) as you maintain brake
application. Then, move the shift lever into
the gear you want.
If you ever hold the brake pedal down but still can
not shift out of PARK (P), try this:
1. Turn the key to ACCESSORY. There is no
shift interlock in this key position.
2. Apply and hold the brake until the end of
Step 4.
3. Shift the transmission to NEUTRAL (N).
4. Start the vehicle and then shift to the gear
you want.
5. Have the system xed as soon as you can.
172

R(On):Move the switch to this position to turn on
the cruise control system.
+ (Resume/Accelerate):Move the switch to this
position to make the vehicle accelerate or
resume to a previously set speed.
T(Set):Press this button to set the speed.
With cruise control, the vehicle can maintain
a speed of about 25 mph (40 km/h) or more
without keeping your foot on the accelerator. This
can really help on long trips. Cruise control
does not work at speeds below about
25 mph (40 km/h).
If you apply your brakes, the cruise control will
shut off.
{CAUTION:
Cruise control can be dangerous where
you cannot drive safely at a steady speed.
So, do not use your cruise control on
winding roads or in heavy traffic.
Cruise control can be dangerous on
slippery roads. On such roads, fast
changes in tire traction can cause
excessive wheel slip, and you could lose
control. Do not use cruise control on
slippery roads.
218

This light should come on briey when you turn
the ignition key to RUN. If it does not come
on then, have it xed so it will be ready to warn
you if there is a problem.
If the light comes on while you are driving, pull off
the road and stop carefully. You may notice
that the pedal is harder to push or may go closer
to the oor. It may take longer to stop. If the
light is still on, have the vehicle towed for service.
SeeTowing Your Vehicle on page 423.
{CAUTION:
Your brake system may not be working
properly if the brake system warning light
is on. Driving with the brake system
warning light on can lead to an accident.
If the light is still on after you have pulled
off the road and stopped carefully, have
the vehicle towed for service.
Anti-Lock Brake System Warning
Light
With the Anti-Lock Brake
System (ABS), this light
will come on when you
start your engine and
may stay on for several
seconds.
That is normal. If the light does not come on then,
have it xed so it will be ready to warn you if
there is a problem.
If the light stays on, or comes on when you are
driving, your vehicle needs service. A chime
will sound when the light stays on. If the regular
brake system warning light is not on, you still have
brakes, but you do not have ABS. If the regular
brake system warning light is also on you do
not have ABS and there is a problem with your
regular brakes. In addition to both lights, you
will also hear a chime sound on the rst
occurrence of a problem and each time the
vehicle is shut off and then restarted. SeeBrake
System Warning Light on page 254.
255

SERVICE BRAKE BOOSTER
{CAUTION:
Your brake system may not be working
properly if the SERVICE BRAKE
BOOSTER message is displayed.
If the brake system warning light is also
on, you should have the vehicle towed for
service. SeeBrake System Warning Light
on page 254.
If the brake system warning light is not
on, you still have brakes, but the
supplemental brake assist system on
vehicles with rear disc brakes may not
operate properly. In the event of a vacuum
loss, you may not have vacuum power
assist for braking. The brake pedal will be
harder to push and it will take longer to
stop. If you continue to drive with this
message displayed it can lead to a crash.
Have the brake system serviced as soon
as possible.If your vehicle has vacuum assist power brakes,
this message will be displayed on the DIC
when there is a problem with the Supplemental
Brake Assist system. If the message is displayed
immediately after starting the vehicle or the
message appears while driving, the Supplemental
Brake Assist system needs service. See your
dealer. SeeBrake System Warning Light on
page 254for additional information.
SERVICE BRAKE SYSTEM
If there is a problem with the brake system, this
message will be displayed on the DIC. If this
message appears, stop as soon as possible and
turn off the vehicle. Restart the vehicle and
check for the message on the DIC display. If the
message is still displayed or appears again
when you begin driving, the brake system needs
service. See your dealer.
278