2009 GMC ENVOY ECU

Rear Towing (Rear Wheels Off the
Ground)Two-Wheel-Drive Vehicles
Use the following procedure to dolly tow a
two-wheel-drive vehicle from the rear:
1. Attach the dolly to the tow vehicle following the
dolly manufacturer’s instructions.
2. Drive the rear wheels onto the dolly.
3. Firmly set the parking brake. SeeParking Brake on
page 2-33.
4. Put the transmission in P (Park).
5. Secure the vehicle to the dolly following the
manufacturer’s instructions.
6. Use an adequate clamping device designed for
towing to ensure that the front wheels are locked
into the straight position.
7. Turn the ignition to LOCK/OFF.
4-43

Four-Wheel-Drive Vehicles
Use the following procedure to dolly tow a
four-wheel-drive vehicle from the rear:
1. Attach the dolly to the tow vehicle following the
dolly manufacturer’s instructions.
2. Drive the rear wheels onto the dolly.
3. Firmly set the parking brake. SeeParking Brake on
page 2-33.
4. Put the transmission in P (Park).
5. Secure the vehicle to the dolly following the
manufacturer’s instructions.
6. Use an adequate clamping device designed for
towing to ensure that the front wheels are locked
into the straight position.{CAUTION:
Shifting a four-wheel-drive vehicle’s transfer case
into N (Neutral) can cause the vehicle to roll even
if the transmission is in P (Park). The driver or
others could be injured. Make sure the parking
brake is rmly set before the transfer case is
shifted to N (Neutral).
7. Shift the transfer case to Neutral. See “Shifting into
Neutral” underFour-Wheel Drive on page 2-28.
8. Turn the ignition to LOCK/OFF.
After towing, see “Shifting Out of Neutral” under
Four-Wheel Drive on page 2-28.
4-44

Look in the following chart to nd the maximum trailer weight for the vehicle.
Vehicle Axle Ratio Max. Trailer Wt. *GCWR
2WD Envoy (4.2 L L6 Engine)3.42 5,300 lbs (2 404 kg) 10,000 lbs (4 536 kg)
3.73 5,800 lbs (2 631 kg) 10,500 lbs (4 763 kg)
4.10 6,300 lbs (2 858 kg) 11,000 lbs (4 990 kg)
2WD Envoy (5.3 L V8 Engine)3.42 6,100 lbs (2 767 kg) 11,000 lbs (4 990 kg)
3.73 6,600 lbs (2 994 kg) 11,500 lbs (5 216 kg)
4WD Envoy (4.2 L L6 Engine)3.42 5,200 lbs (2 359 kg) 10,000 lbs (4 536 kg)
3.73 5,700 lbs (2 858 kg) 10,500 lbs (4 763 kg)
4.10 6,200 lbs (2 812 kg) 11,000 lbs (4 990 kg)
4WD Envoy (5.3 L V8 Engine)3.42 6,000 lbs (2 721 kg) 11,000 lbs (4 990 kg)
3.73 6,500 lbs (2 948 kg) 11,500 lbs (5 216 kg)
*The Gross Combination Weight Rating (GCWR) is the total allowable weight of the completely loaded vehicle and
trailer including any passengers, cargo, equipment and conversion. The GCWR for the vehicle should not be
exceeded.
Ask your dealer for our trailering information or advice, or write us at our Customer Assistance Offices. SeeCustomer
Assistance Offices on page 7-6for more information.
4-48

Driving with a Trailer
{CAUTION:
When towing a trailer, exhaust gases may collect
at the rear of the vehicle and enter if the liftgate,
trunk/hatch, or rear-most window is open.
Engine exhaust contains carbon monoxide (CO)
which cannot be seen or smelled. It can cause
unconsciousness and even death.
To maximize safety when towing a trailer:
Have the exhaust system inspected for leaks
and make necessary repairs before starting
a trip.
Never drive with the liftgate, trunk/hatch, or
rear-most window open.
Fully open the air outlets on or under the
instrument panel.
Adjust the Climate Control system to a setting
that brings in only outside air and set the fan
speed to the highest setting. See Climate
Control System in the Index.
For more information about carbon monoxide, see
Engine Exhaust on page 2-37.Towing a trailer requires a certain amount of experience.
Get to know the rig before setting out for the open road.
Get acquainted with the feel of handling and braking with
the added weight of the trailer. And always keep in mind
that the vehicle you are driving is now longer and not as
responsive as the vehicle is by itself.
Before starting, check all trailer hitch parts and
attachments, safety chains, electrical connectors, lamps,
tires and mirror adjustments. If the trailer has electric
brakes, start the vehicle and trailer moving and then
apply the trailer brake controller by hand to be sure the
brakes are working. This checks the electrical connection
at the same time.
During the 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 the vehicle without a trailer.
This can help to avoid situations that require heavy
braking and sudden turns.
Passing
More passing distance is needed when towing a trailer.
Because the rig is longer, it is necessary to go much
farther beyond the passed vehicle before returning to
the lane.
4-53

6. Start the engine and let it run until you can feel the
upper radiator hose getting hot. Watch out for the
engine cooling fan.
7. By this time, the coolant level inside the radiator
ller neck may be lower. If the level is lower, add
more of the proper DEX-COOL coolant mixture
through the ller neck until the level reaches
the base of the ller neck.8. Then replace the pressure cap. At any time during
this procedure if coolant begins to ow out of the
ller neck, reinstall the pressure cap. Be sure
the pressure cap is hand-tight and fully seated.
Notice:If the pressure cap is not tightly installed,
coolant loss and possible engine damage may occur.
Be sure the cap is properly and tightly secured.
Engine Overheating
The vehicle has several indicators to warn of engine
overheating.
You will nd a coolant temperature gage on the vehicle’s
instrument panel. SeeEngine Coolant Temperature
Gage on page 3-37for more information.
If the vehicle has a Driver Information Center (DIC), the
display will show an Engine Coolant Hot/Engine
Overheated message. SeeDIC Warnings and Messages
on page 3-51for more information.
5-30

Bulb Replacement
For the proper type of replacement bulbs, see
Replacement Bulbs on page 5-49.
For any bulb changing procedure not listed in this
section, contact your dealer/retailer.
Halogen Bulbs
{CAUTION:
Halogen bulbs have pressurized gas inside and
can burst if you drop or scratch the bulb. You or
others could be injured. Be sure to read and follow
the instructions on the bulb package.
Headlamps
To replace one of these bulbs:
1. Open the hood.Hood Release on page 5-11.
2. Lift the two headlamp retaining clips.3. Pull the headlamp assembly away from the vehicle
to access the electrical connectors.
4. Remove the cover from the headlamp bulb.
5. Turn the bulb socket counterclockwise and remove it.
6. Disconnect the electrical connector from the old bulb.
7. Plug the electrical connector into the new bulb using
care not to touch the glass with your ngers.
8. Turn the socket clockwise to reinstall it.
9. Reinstall the headlamp cover.
10. Push the headlamp assembly toward the vehicle.
11. Press down on the headlamp retaining clips to
secure the headlamp assembly.
5-46

Front Turn Signal, Sidemarker and
Parking Lamps
To replace one of these bulbs:
1. Follow Steps 1 through 3 underHeadlamps on
page 5-46to access the front turn signal,
sidemarker or parking lamp.
2. Turn the bulb socket counterclockwise and remove
it from the lamp assembly.
3. Holding the socket, pull the old bulb to release it
from the socket.
4. Push the new bulb into the socket until it clicks.
5. Insert the bulb socket into the lamp assembly and
turn it clockwise to secure.
6. Reinstall the headlamp assembly by lining up the
headlamp assembly with the slots in the headlamp
retaining clips.
7. Press down on the headlamp retaining clips to
secure the headlamp assembly.
Taillamps, Turn Signal, and
Stoplamps
To replace a stoplamp/taillamp or turn signal bulb:
1. Open the liftgate. SeeLiftgate/Liftglass on
page 2-12.
2. Remove the
two screws from
the taillamp
assembly.
3. Pull the assembly away from the vehicle.
5-47

4. Unclip the wiring harness (A) and remove the three
socket retaining screws (B).
5. Remove the socket plate.
6. Holding the socket, pull the bulb to straight out
release it from the socket.
7. Push the new bulb into the socket until it clicks.
8. Reinstall the socket plate and three screws.
9. Reconnect the wiring harness.
10. Reinstall the taillamp assembly by lining up the
locator pins with the retainers in the body of the
vehicle.
11. Reinstall the two screws.
Back-Up Lamps
The back-up lamps are located in the rear bumper.
To replace a bulb:
1. Reach behind the rear bumper and locate the bulb
socket.
2. Turn it counterclockwise to remove from the lamp
assembly.
3. Holding the socket, pull the old bulb to release it
from the socket.
4. Push in a new bulb into the bulb socket until it
clicks.
5. Reinstall the bulb socket into the lamp assembly
and turn it clockwise to secure.
5-48