notice a slight audible knocking noise, commonly referred
to as spark knock. If the octane is less than 87, you might
notice a heavy knocking noise when you drive. If this
occurs, use a gasoline rated at 87 octane or higher as
soon as possible. Otherwise, you could damage the
engine. If you are using gasoline rated at 87 octane or
higher and you hear heavy knocking, the engine needs
service.
Gasoline Speci cations
At a minimum, gasoline should meet ASTM speci cation
D 4814 in the United States or CAN/CGSB-3.5 or 3.511 in
Canada. Some gasolines contain an octane-enhancing
additive called methylcyclopentadienyl manganese
tricarbonyl (MMT). We recommend against the use of
gasolines containing MMT. SeeAdditives on page 5-7
for additional information.
California Fuel
If the vehicle is certi ed to meet California Emissions
Standards, it is designed to operate on fuels that meet
California speci cations. See the underhood emission
control label. If this fuel is not available in states adopting
California emissions standards, the vehicle will operate
satisfactorily on fuels meeting federal speci cations, but
emission control system performance might be affected.
The malfunction indicator lamp could turn on and the
vehicle might fail a smog-check test. SeeMalfunctionIndicator Lamp on page 3-45. If this occurs, return to your
authorized dealer/retailer for diagnosis. If it is determined
that the condition is caused by the type of fuel used,
repairs might not be covered by the vehicle warranty.
Additives
To provide cleaner air, all gasolines in the United States
are now required to contain additives that help prevent
engine and fuel system deposits from forming, allowing
the emission control system to work properly. In most
cases, you should not have to add anything to the fuel.
However, some gasolines contain only the minimum
amount of additive required to meet U.S. Environmental
Protection Agency regulations. To help keep fuel injectors
and intake valves clean, or if the vehicle experiences
problems due to dirty injectors or valves, look for gasoline
that is advertised as TOP TIER Detergent Gasoline.
For customers who do not use TOP TIER Detergent
Gasoline regularly, one bottle of GM Fuel System
Treatment PLUS, added to the fuel tank at every engine
oil change, can help clean deposits from fuel injectors
and intake valves. GM Fuel System Treatment PLUS
is the only gasoline additive recommended by General
Motors.
Also, your dealer/retailer has additives that will help
correct and prevent most deposit-related problems.
5-7 
{CAUTION:
Fuel can spray out on you if you open the fuel cap
too quickly. If you spill fuel and then something
ignites it, you could be badly burned. This spray
can happen if the tank is nearly full, and is more
likely in hot weather. Open the fuel cap slowly and
wait for any hiss noise to stop. Then unscrew the
cap all the way.
If the vehicle is a dual fuel tank chassis cab model, and
it runs out of fuel, refuel the front fuel tank  rst to
ensure a quick restart.
Be careful not to spill fuel. Do not top off or over ll the
tank and wait a few seconds after you have  nished
pumping before removing the nozzle. Clean fuel from
painted surfaces as soon as possible. SeeWashing
Your Vehicle on page 5-118.
When replacing the fuel cap, turn it clockwise until it
clicks. It will require more effort to turn the fuel cap on
the last turn as you tighten it. Make sure the cap is
fully installed. The diagnostic system can determine ifthe fuel cap has been left off or improperly installed.
This would allow fuel to evaporate into the atmosphere.
SeeMalfunction Indicator Lamp on page 3-45.
The TIGHTEN GAS CAP message displays on the Driver
Information Center (DIC) if the fuel cap is not properly
installed. SeeDIC Warnings and Messages on page 3-66
for more information.
{CAUTION:
If a  re starts while you are refueling, do not
remove the nozzle. Shut off the  ow of fuel by
shutting off the pump or by notifying the station
attendant. Leave the area immediately.
Notice:If you need a new fuel cap, be sure to get
the right type. Your dealer/retailer can get one
for you. If you get the wrong type, it may not  t
properly. This may cause the malfunction indicator
lamp to light and may damage the fuel tank and
emissions system. SeeMalfunction Indicator Lamp
on page 3-45.
5-11 
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.
Bulb Replacement
For the proper type of replacement bulbs, see
Replacement Bulbs on page 5-63.
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. SeeHood Release on page 5-13
for more information.
2. If you are replacing the bulb on the passenger side
remove the Engine Air Cleaner cover. SeeEngine Air
Cleaner/Filter on page 5-19for more information.
3. Reach in and access the bulb sockets from inside
the engine compartment.
5-58 
Windshield Wiper Blade
Replacement
Windshield wiper blades should be inspected for wear
or cracking. SeeScheduled Maintenance (Gasoline
Engine) on page 6-4for more information on wiper blade
inspection.
Replacement blades come in different types and are
removed in different ways. Here is how to remove
the wiper blade:
1. Pull the windshield wiper arm connector away from
the windshield.
2. Squeeze the grooved areas on each side of the
blade and turn the blade assembly away from the
arm connector.3. Install the new blade onto the arm connector and
make sure the grooved areas are fully set in the
locked position.
For the proper type and size, seeMaintenance
Replacement Parts on page 6-17.
5-64