2007 GMC YUKON XL headlamp

No one can see as well at night as in the daytime.
But as we get older these differences increase.
A 50-year-old driver may require at least twice as
much light to see the same thing at night as a
20-year-old.
What you do in the daytime can also affect your
night vision. For example, if you spend the
day in bright sunshine you are wise to wear
sunglasses. Your eyes will have less trouble
adjusting to night. But if you are driving, do not
wear sunglasses at night. They may cut down on
glare from headlamps, but they also make a
lot of things invisible.
You can be temporarily blinded by approaching
headlamps. It can take a second or two, or
even several seconds, for your eyes to re-adjust
to the dark. When you are faced with severe glare,
as from a driver who does not lower the high
beams, or a vehicle with misaimed headlamps,
slow down a little. Avoid staring directly into
the approaching headlamps.Keep the windshield and all the glass on your
vehicle clean — inside and out. Glare at night is
made much worse by dirt on the glass. Even
the inside of the glass can build up a lm caused
by dust. Dirty glass makes lights dazzle and
ash more than clean glass would, making the
pupils of your eyes contract repeatedly.
Remember that the headlamps light up far less
of a roadway when you are in a turn or curve.
Keep your eyes moving; that way, it is easier to
pick out dimly lighted objects. Just as the
headlamps should be checked regularly for
proper aim, so should your eyes be examined
regularly. Some drivers suffer from night
blindness — the inability to see in dim
light — and are not even aware of it.
374

Driving Through Deep Standing Water
Notice:If you drive too quickly through deep
puddles or standing water, water can come in
through your engine’s air intake and badly
damage your engine. Never drive through water
that is slightly lower than the underbody of your
vehicle. If you cannot avoid deep puddles or
standing water, drive through them very slowly.
Driving Through Flowing Water
{CAUTION:
Flowing or rushing water creates strong
forces. If you try to drive through owing
water, as you might at a low water
crossing, your vehicle can be carried away.
As little as six inches of owing water can
carry away a smaller vehicle. If this
happens, you and other vehicle occupants
could drown. Do not ignore police warning
signs, and otherwise be very cautious
about trying to drive through owing water.
Some Other Rainy Weather Tips
Turn on your low-beam headlamps — not just
your parking lamps — to help make you more
visible to others.
Besides slowing down, allow some extra
following distance. And be especially careful
when you pass another vehicle. Allow yourself
more clear room ahead, and be prepared to
have your view restricted by road spray.
Have good tires with proper tread depth. See
Tires on page 482.
377

{CAUTION:
Snow can trap exhaust gases under your
vehicle. This can cause deadly CO
(carbon monoxide) gas to get inside.
CO could overcome you and kill you.
You cannot see it or smell it, so you might
not know it is in your vehicle. Clear away
snow from around the base of your
vehicle, especially any that is blocking
your exhaust pipe. And check around
again from time to time to be sure snow
does not collect there.
Open a window just a little on the side of
the vehicle that is away from the wind.
This will help keep CO out.Run your engine only as long as you must. This
saves fuel. When you run the engine, make it go a
little faster than just idle. That is, push the
accelerator slightly. This uses less fuel for the
heat that you get and it keeps the battery charged.
You will need a well-charged battery to restart
the vehicle, and possibly for signaling later on with
your headlamps. Let the heater run for a while.
Then, shut the engine off and close the window
almost all the way to preserve the heat. Start
the engine again and repeat this only when you
feel really uncomfortable from the cold. But do it as
little as possible. Preserve the fuel as long as
you can. To help keep warm, you can get out of
the vehicle and do some fairly vigorous exercises
every half hour or so until help comes.
387

Heavy-Duty Trailer Wiring Harness
Package
Your vehicle is equipped with the seven-wire
trailer towing harness. This harness with a
seven-pin universal trailer connector is attached to
a bracket on the hitch platform.
The seven-wire harness contains the following
trailer circuits:
Yellow: Left Stop/Turn Signal
Dark Green: Right Stop/Turn Signal
Brown: Taillamps
White: Ground
Light Green: Back-up Lamps
Red: Battery Feed*
Dark Blue: Trailer Brake*
*The fuses for these two circuits are installed in
the underhood electrical center, but the wires
are not connected. They should be connected by
your dealer or a qualied service center.
If you are charging a remote (non-vehicle) battery,
press the tow/haul mode button located at the
end of the shift lever. This will boost the vehicle
system voltage and properly charge the battery. If
the trailer is too light for tow/haul mode, you
can turn on the headlamps as a second way to
boost the vehicle system and charge the battery.
421

Service.........................................................426
Accessories and Modications....................426
California Proposition 65 Warning...............427
Doing Your Own Service Work...................427
Adding Equipment to the Outside of
Your Vehicle...........................................428
Fuel..............................................................428
Gasoline Octane........................................428
Gasoline Specications...............................428
California Fuel............................................429
Additives....................................................429
Fuel E85 (85% Ethanol).............................430
Fuels in Foreign Countries.........................431
Filling the Tank..........................................432
Filling a Portable Fuel Container................434
Checking Things Under the Hood..............434
Hood Release............................................435
Engine Compartment Overview...................436
Engine Oil..................................................438
Engine Oil Life System...............................441
Engine Air Cleaner/Filter.............................443
Automatic Transmission Fluid.....................445
Engine Coolant...........................................449Coolant Surge Tank Pressure Cap.............451
Engine Overheating....................................452
Overheated Engine Protection
Operating Mode......................................454
Cooling System..........................................455
Engine Fan Noise......................................460
Power Steering Fluid..................................461
Windshield Washer Fluid............................462
Brakes.......................................................463
Battery.......................................................466
Jump Starting.............................................467
Rear Axle.....................................................472
Four-Wheel Drive.........................................473
Front Axle....................................................474
Headlamp Aiming........................................475
Bulb Replacement........................................478
Halogen Bulbs............................................478
Taillamps, Turn Signal, Stoplamps and
Back-up Lamps.......................................478
License Plate Lamp....................................480
Replacement Bulbs....................................481
Section 5 Service and Appearance Care
423

What to Use
Refer to the Maintenance Schedule to determine
what kind of lubricant to use. SeeRecommended
Fluids and Lubricants on page 564.
Headlamp Aiming
The vehicle has a visual optical headlamp aiming
system. The aim of the headlamps have been
preset at the factory and should need no further
adjustment.
However, if the vehicle is damaged in an accident,
the aim of the headlamps may be affected and
adjustment may be necessary.
If oncoming vehicles ash their high beams at
you, this may mean the vertical aim of your
headlamps needs to be adjusted.
It is recommended that the vehicle is taken to your
dealer for service if the headlamps need to be
adjusted. It is possible however, to re-aim
the headlamps as described in the following
procedure.The vehicle should be properly prepared as
follows:
The vehicle should be placed so the
headlamps are 25 ft. (7.6 m) from a light
colored wall.
The vehicle must have all four tires on a level
surface which is level all the way to the wall.
The vehicle should be placed so it is
perpendicular to the wall.
The vehicle should not have any snow, ice, or
mud on it.
The vehicle should be fully assembled and all
other work stopped while headlamp aiming is
being performed.
The vehicle should be normally loaded with
a full tank of fuel and one person or
160 lbs (75 kg) sitting on the driver’s seat.
Tires should be properly inated.
The spare tire is in its proper location in the
vehicle.
Headlamp aiming is done with the vehicle’s
low-beam headlamps. The high-beam headlamps
will be correctly aimed if the low-beam headlamps
are aimed properly.
475

To adjust the vertical aim, do the following:
1. Open the hood. SeeHood Release on
page 435for more information.
2. Locate the aim dot on the lens of the
low-beam headlamp.
3. Measure the distance from the ground to the
aim dot on the low-beam headlamp. Record
the distance.4. At the wall or other at surface, measure from
the ground upward (A) to the recorded
distance from Step 3 and mark it.
5. Draw or tape a horizontal line (B) on the wall
or at surface the width of the vehicle at the
height of the mark in Step 4.
Notice:Do not cover a headlamp to improve
beam cut-off when aiming. Covering a
headlamp may cause excessive heat build-up
which may cause damage to the headlamp.
6. Turn on the low-beam headlamps and place a
piece of cardboard or equivalent in front of the
headlamp not being adjusted. This allows
only the beam of light from the headlamp
being adjusted to be seen on the at surface.
476

7. Locate the vertical headlamp aiming screws,
which are under the hood near each headlamp
assembly.
The adjustment screw can be turned with a
E8 Torx
®socket.
8. Turn the vertical aiming screw until the
headlamp beam is aimed to the horizontal
tape line. Turn it clockwise or
counterclockwise to raise or lower the angle
of the beam.9. Make sure that the light from the headlamp is
positioned at the bottom edge of the horizontal
tape line. The lamp on the left (A) shows
the correct headlamp aim. The lamp on the
right (B) shows the incorrect headlamp aim.
10. Repeat Steps 7 through 9 for the opposite
headlamp.
477