Chevrolet Silverado Classic 2007 Owner's Manual page 260

If the Light Is On Steady
You may be able to correct the emission system
malfunction by considering the following:
Did you recently put fuel into your vehicle?
If so, reinstall the fuel cap, making sure to fully
install the cap. See Filling the Tank on page 475.
The diagnostic system can determine if the
fuel cap has been left off or improperly installed.
A loose or missing fuel cap will allow fuel to
evaporate into the atmosphere. A few driving
trips with the cap properly installed should
turn the light off.
Did you just drive through a deep puddle
of water?
If so, your electrical system may be wet.
The condition will usually be corrected when
the electrical system dries out. A few driving
trips should turn the light off.
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Have you recently changed brands of fuel?
If so, be sure to fuel your vehicle with quality fuel.
See Gasoline Octane on page 471. Poor fuel
quality will cause your engine not to run as
efficiently as designed. You may notice this as
stalling after start-up, stalling when you put
the vehicle into gear, misfiring, hesitation on
acceleration, or stumbling on acceleration.
(These conditions may go away once the
engine is warmed up.) This will be detected
by the system and cause the light to turn on.
If you experience one or more of these conditions,
change the fuel brand you use. It will require
at least one full tank of the proper fuel to turn
the light off.
If none of the above steps have made the light
turn off, your dealer can check the vehicle.
Your dealer has the proper test equipment
and diagnostic tools to fix any mechanical or
electrical problems that may have developed.