2000 GMC ENVOY stop start

4-48
Tow/Haul Mode
The Tow/Haul Mode is a feature that assists when
pulling a heavy trailer. The purpose of the Tow/Haul
Mode is:

Reduce the frequency of shifts when pulling a
heavy trailer.

Provide the same shift feel when pulling a heavy
trailer as when the vehicle is unloaded.

Reduce the need to change throttle positions when
pulling a heavy trailer.
This feature is turned on or off by pressing a button on
the shift lever. When the feature is on, a light on the
instrument panel will illuminate to indicate that the
Tow/Haul Mode has been selected. See ªTow/Haul
Mode Lightº in the Index. The Tow/Haul Mode is
automatically turned off each time the vehicle is started.
The Tow/Haul Mode is most effective when the vehicle
and trailer combined weight is at least 75% of the Gross
Vehicle Weight Rating (GVWR) and the maximum
trailer weight rating for the vehicle. See ªGross Vehicle
Weight Ratingº and ªTrailer Weightº in the Index.The Tow/Haul Mode for hauling a heavy trailer is most
useful under the following conditions:

When driving through hilly terrain at high speeds
below 55 mph (88 km/h).

When driving in low speed or stop and go traffic
below 55 mph (88 km/h).

When driving in parking lots.
Use the Tow/Haul Mode instead of the previous
recommendation to shift to THIRD (3) to improve fuel
economy at highway speeds and shift performance at
lower speeds. Operating in the Tow/Haul Mode when
not pulling a heavy trailer will not cause damage to the
vehicle, but you may experience reduced fuel economy
and undesirable performance from the engine and
transmission. The Tow/Haul Mode should be used only
when pulling a heavy trailer.
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4-54 Turn Signals When Towing a Trailer
When you tow a trailer, your vehicle has to have extra
wiring and a heavy
-duty turn signal flasher.
The arrows on your instrument panel will flash
whenever you signal a turn or lane change. Properly
hooked up, the trailer lamps will also flash, telling other
drivers you're about to turn, change lanes or stop.
When towing a trailer, the arrows on your instrument
panel will flash for turns even if the bulbs on the trailer
are burned out. Thus, you may think drivers behind you
are seeing your signal when they are not. It's important
to check occasionally to be sure the trailer bulbs are
still working.
Driving On Grades
Reduce speed and shift to a lower gear before you start
down a long or steep downgrade. If you don't shift
down, you might have to use your brakes so much
that they would get hot and no longer work well.You should use THIRD (3) when towing a trailer.
Operating your vehicle in THIRD (3) when towing a
trailer will minimize heat buildup and extend the life of
your transmission. See ªTow/Haul Modeº in the Index.
When towing at high altitude on steep uphill grades,
consider the following: Engine coolant will boil at a
lower temperature than at normal altitudes. If you turn
your engine off immediately after towing at high altitude
on steep uphill grades, your vehicle may show signs
similar to engine overheating. To avoid this, let the
engine run while parked (preferably on level ground)
with the automatic transmission in PARK (P) for a few
minutes before turning the engine off. If you do get the
overheat warning, see ªEngine Overheatingº in
the Index.
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4-56 When You Are Ready to Leave After
Parking on a Hill
1. Apply your regular brakes and hold the pedal down
while you:

Start your engine;

Shift into a gear; and

Release the parking brake.
2. Let up on the brake pedal.
3. Drive slowly until the trailer is clear of the chocks.
4. Stop and have someone pick up and store the chocks.
Maintenance When Trailer Towing
Your vehicle will need service more often when you're
pulling a trailer. See the Maintenance Schedule for more
on this. Things that are especially important in trailer
operation are automatic transmission fluid (don't
overfill), engine oil, axle lubricant, belt, cooling system
and brake system. Each of these is covered in this
manual, and the Index will help you find them quickly.
If you're trailering, it's a good idea to review these
sections before you start your trip.
Check periodically to see that all hitch nuts and bolts
are tight.
Trailer Wiring Harness
The heavy-duty trailer wiring is an eight-wire harness
assembly. The harness is stored under the vehicle, on the
driver's side corner frame rear crossmember. The harness is
fused in the engine compartment fuse block. See ªFuses and
Circuit Breakersº in the Index. The harness does not have a
connector and should be wired by a qualified electrical
technician. The technician can use the following color code
chart when connecting the wiring harness to your trailer.

Dark Blue: Use for electric trailer brakes or
auxiliary wiring.

Red: Use for battery charging; it connects to the
starter solenoid.

Light Green: Back
-up lamps.

Brown: Taillamps and parking lamps.

Yellow: Left stoplamp and turn signal.

Dark Green: Right stoplamp and turn signal.

White: Ground wire.

Light Blue: Auxiliary stoplamp.
Securely attach the harness to the trailer, then tape or
strap it to your vehicle's frame rail. Be sure you leave it
loose enough so the wiring doesn't bend or break, but
not so loose that it drags on the ground. Store the
harness in its original place. Wrap the harness together
and tie it neatly so it won't be damaged.
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5-19
Engine Fan Noise
This vehicle has a clutched engine cooling fan. When
the clutch is engaged, the fan spins faster to provide
more air to cool the engine. In most everyday driving
conditions, the clutch is not engaged. This improves fuel
economy and reduces fan noise. Under heavy vehicle
loading, trailer towing and/or high outside temperatures,
the fan speed increases when the clutch engages. So you
may hear an increase in fan noise. This is normal and
should not be mistaken as the transmission slipping or
making extra shifts. It is merely the cooling system
functioning properly. The fan will slow down when
additional cooling is not required and the
clutch disengages.
You may also hear this fan noise when you start the
engine. It will go away as the fan clutch disengages.
If a Tire Goes Flat
It's unusual for a tire to ªblow outº while you're driving,
especially if you maintain your tires properly. If air goes
out of a tire, it's much more likely to leak out slowly.
But if you should ever have a ªblowout,º here are a few
tips about what to expect and what to do:
If a front tire fails, the flat tire will create a drag that
pulls the vehicle toward that side. Take your foot off
the accelerator pedal and grip the steering wheel firmly.
Steer to maintain lane position, and then gently brake
to a stop well out of the traffic lane.
A rear blowout, particularly on a curve, acts much like a
skid and may require the same correction you'd use in
a skid. In any rear blowout, remove your foot from
the accelerator pedal. Get the vehicle under control by
steering the way you want the vehicle to go. It may
be very bumpy and noisy, but you can still steer.
Gently brake to a stop
-- well off the road if possible.
If a tire goes flat, the next part shows how to use your
jacking equipment to change a flat tire safely.
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6-13
As shown in the chart, SAE 5W-30 is best for your
vehicle. However, you can use SAE 10W
-30 if it's going
to be 0F (
-18C) or above. These numbers on an oil
container show its viscosity, or thickness. Do not use
other viscosity oils, such as SAE 20W
-50.
NOTICE:
Use only engine oil with the American Petroleum
Institute Certified For Gasoline Engines starburst
symbol. Failure to use the recommended oil
can result in engine damage not covered by
your warranty.
GM Goodwrench oil meets all the requirements for
your vehicle.
If you are in an area where the temperature falls below
-20F (-29C), consider using either an SAE 5W-30
synthetic oil or an SAE 0W
-30 oil. Both will provide
easier cold starting and better protection for your engine
at extremely low temperatures.
Engine Oil Additives
Don't add anything to your oil. The recommended oils
with the starburst symbol are all you will need for good
performance and engine protection.
When to Change Engine Oil
If any one of these is true for you, use the short trip/city
maintenance schedule:

Most trips are less than 5 to 10 miles (8 to 16 km).
This is particularly important when outside
temperatures are below freezing.

Most trips include extensive idling (such as frequent
driving in stop
-and-go traffic).

You operate your vehicle in dusty areas or
off
-road frequently.

You frequently tow a trailer or use a carrier on
top of your vehicle.

The vehicle is used for delivery service, police, taxi
or other commercial application.
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