2004 GMC SONOMA towing

If You Do Decide To Pull A Trailer
If you do, here are some important points:
•There are many different laws, including speed limit
restrictions, having to do with trailering. Make sure
your rig will be legal, not only where you live
but also where you’ll be driving. A good source for
this information can be state or provincial police.
•Consider using a sway control. See “Hitches” later
in this section.
•Don’t tow a trailer at all during the first 500 miles
(800 km) your new vehicle is driven. Your engine,
axle or other parts could be damaged.
•Then, during the first 500 miles (800 km) that you
tow a trailer, don’t drive over 50 mph (80 km/h)
and don’t make starts at full throttle. This helps your
engine and other parts of your vehicle wear in at
the heavier loads.
•You may want to shift the transmission to THIRD (3)
or, if necessary, a lower gear selection if the
transmission shifts too often (e.g., under heavy
loads and/or hilly conditions). If you have a manual
transmission and you are towing a trailer, it’s
better not to use the highest gear.Three important considerations have to do with weight:
•the weight of the trailer,
•the weight of the trailer tongue
•and the weight on your vehicle’s tires.
Weight of the Trailer
How heavy can a trailer safely be?
It depends on how you plan to use your rig. For
example, speed, altitude, road grades, outside
temperature and how much your vehicle is used to pull
a trailer are all important. And, it can also depend
on any special equipment that you have on your vehicle.
The following chart shows how much your trailer can
weigh, based upon your vehicle model and options.
Maximum trailer weight is calculated assuming only the
driver is in the tow vehicle and it has all the required
trailering equipment. The weight of additional optional
equipment, passengers and cargo in the tow vehicle
must be subtracted from the maximum trailer weight.
The weight of the trailer tongue also affects trailering
capacity. See “Weight of the Trailer Tongue” next.
4-56

If you’ll be pulling a trailer, that when loaded, will weigh
more than 5,000 lbs (2 270 kg) be sure to use a
properly mounted weight-distributing hitch and sway
control of the proper size. This equipment is very
important for proper vehicle loading and good handling
when driving. You should always use a sway control
if your traile will weigh more than these limits. You can
ask a hitch dealer about sway controls.
Safety Chains
You should always attach chains between your vehicle
and your trailer. Cross the safety chains under the
tongue of the trailer to help prevent the tongue from
contacting the road if it becomes separated from
the hitch. Instructions about safety chains may be
provided by the hitch manufacturer or by the trailer
manufacturer. For trailers up to 3,500 lbs. (1 589 kg) you
may attach the safety chains to the attaching points
on the bumper. For heavier trailers, follow the trailer or
hitch manufacturer’s recommendation for attaching
safety chains. Always leave just enough slack so you
can turn with your rig. Never allow safety chains to drag
on the ground.
Trailer Brakes
If your trailer weighs more than 1,000 lbs. (450 kg)
loaded, then it needs its own brake–and they must be
adequate. Be sure to read and follow the instructions for
the trailer brakes so you’ll be able to install, adjust
and maintain them properly.
Your trailer’s brake system can tap into the vehicle’s
hydraulic brake system only if:
•The trailer parts can withstand 3,000 psi
(20 650 kPa) of pressure.
•The trailer’s brake system will use less than
0.02 cubic inch (0.3 cc) of fluid from your vehicle’s
master cylinder. Otherwise, both braking systems
won’t work well. You could even lose your brakes.
If everything checks out this far, then make the brake
fluid tap at the port on the master cylinder that
sends fluid to the rear brakes. But don’t use copper
tubing for this. If you do, it will bend and finally break off.
Use steel brake tubing.
Driving with a Trailer
Towing a trailer requires a certain amount of experience.
Before setting out for the open road, you’ll want to get
to know your rig. Acquaint yourself with the feel of
handling and braking with the added weight of the trailer.
4-60

And always keep in mind that the vehicle you are
driving is now a good deal longer and not nearly as
responsive as your vehicle is by itself.
Before you start, check all trailer hitch, all parts and
attachments, safety chains, electrical connector, lamps,
tires and mirror adjustment. If the trailer has electric
brakes, start your vehicle and trailer moving and then
apply the trailer brake controller by hand to be sure
the brakes are working. This lets you check your
electrical connection at the same time.
During your trip, check occasionally to be sure that the
load is secure, and that the lamps and any trailer
brakes are still working.
Following Distance
Stay at least twice as far behind the vehicle ahead as
you would when driving your vehicle without a trailer.
This can help you avoid situations that require
heavy braking and sudden turns.
Passing
You’ll need more passing distance up ahead when
you’re towing a trailer. And, because you’re a good deal
longer, you’ll need to go much farther beyond the
passed vehicle before you can return to your lane.
Backing Up
Hold the bottom of the steering wheel with one hand.
Then, to move the trailer to the left, just move that hand
to the left. To move the trailer to the right, move your
hand to the right. Always back up slowly and, if possible,
have someone guide you.
Making Turns
Notice:Making very sharp turns while trailering
could cause the trailer to come in contact with the
vehicle. Your vehicle could be damaged. Avoid
making very sharp turns while trailering.
When you’re turning with a trailer, make wider turns
than normal. Do this so your trailer won’t strike
soft shoulders, curbs, road signs, trees or other objects.
Avoid jerky or sudden maneuvers. Signal well in
advance.
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.
4-61

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.
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) (or
the manual transmission out of gear and the parking
brake applied) for a few minutes before turning the
engine off. If you do get the overheat warning,
seeEngine Overheating on page 5-26.
Parking on Hills
{CAUTION:
You really should not park your vehicle, with a
trailer attached, on a hill. If something goes
wrong, your rig could start to move. People
can be injured, and both your vehicle and the
trailer can be damaged.
But if you ever have to park your rig on a hill, here’s
how to do it:
1. Apply your regular brakes, but don’t shift into
PARK (P) yet, or into gear for a manual
transmission. When parking uphill, turn your wheels
away from the curb. When parking downhill, turn
your wheels into the curb.
2. Have someone place chocks under the
trailer wheels.
3. When the wheel chocks are in place, release the
regular brakes until the chocks absorb the load.
4-62

4. Reapply the regular brakes. Then apply your
parking brake, and then shift into PARK (P), or
REVERSE (R) for a manual transmission.
5. If you have a four-wheel-drive vehicle with an
automatic transfer case, be sure the transfer case is
in a drive gear–not in NEUTRAL.
6. Release the regular brakes.
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. SeePart A: Scheduled Maintenance
Services on page 6-4for 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.
4-63

{CAUTION:
Operating the engine with the air cleaner/lter
off can cause you or others to be burned. The
air cleaner not only cleans the air, it helps to
stop ame if the engine backres. If it is not
there and the engine backres, you could be
burned. Do not drive with it off, and be careful
working on the engine with the air cleaner/
lter off.
Notice:If the air cleaner/lter is off, a backre can
cause a damaging engine re. And, dirt can
easily get into your engine, which will damage it.
Always have the air cleaner/lter in place when you
are driving.
Automatic Transmission Fluid
When to Check and Change the
Automatic Transmission Fluid
A good time to check your automatic transmission fluid
level is when the engine oil is changed.
Change both the fluid and filter every 15,000 miles
(25 000 km) if the vehicle is mainly driven under one or
more of these conditions:
•In heavy city traffic where the outside temperature
regularly reaches 90°F (32°C) or higher.
•In hilly or mountainous terrain.
•When doing frequent trailer towing.
•Uses such as found in taxi, police or delivery
service.
If you do not use your vehicle under any of these
conditions, change the fluid and filter every 50,000 miles
(83 000 km).
SeePart A: Scheduled Maintenance Services on
page 6-4.
5-19

If No Steam Is Coming From Your
Engine
If you get an engine overheat warning but see or hear
no steam, the problem may not be too serious.
Sometimes the engine can get a little too hot when you:
•Climb a long hill on a hot day.
•Stop after high-speed driving.
•Idle for long periods in traffic.
•Tow a trailer. See “Driving on Grades” under
Towing a Trailer on page 4-55.
If you get the overheat warning with no sign of steam,
try this for a minute or so:
1. In heavy traffic, let the engine idle in NEUTRAL
while stopped. If it is safe to do so, pull off the
road, shift to PARK (P) or NEUTRAL and let the
engine idle.
2. Turn on your heater to full hot at the highest fan
speed and open the window as necessary.If you no longer have the overheat warning, you can
drive. Just to be safe, drive slower for about 10 minutes.
If the warning doesn’t come back on, you can drive
normally.
If the warning continues, pull over, stop, and park your
vehicle right away.
If there’s still no sign of steam, idle the engine for three
minutes while you’re parked. Push down the accelerator
until the engine speed is about twice as fast as
normal idle speed for at least three minutes while you’re
parked. If you still have the warning,turn off the
engine and get everyone out of the vehicleuntil it
cools down.
You may decide not to lift the hood but to get service
help right away.
5-27

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.
Power Steering Fluid
The power steering reservoir is located near the front of
the engine compartment on the driver’s side of the
vehicle.
When to Check Power Steering Fluid
It is not necessary to regularly check power steering fluid
unless you suspect there is a leak in the system or
you hear an unusual noise. A fluid loss in this system
could indicate a problem. Have the system inspected
and repaired. SeeEngine Compartment Overview
on page 5-12for reservoir location.
5-35