Voltmeter Gage - Chevrolet 2002 TrailBlazer Owner's Manual

Charging System Indicator Light
It should go out once the engine is running. If it stays
on, or comes on while you are driving, you may have
a problem with the charging system. It could indicate
that you have problems with a generator drive belt, or
another electrical problem. Have it checked right away.
Driving while this light is on could drain your battery.
If you must drive a short distance with the light on, be
certain to turn off all your accessories, such as the radio
and air conditioner.
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The charging system light
will come on briefly when
you turn on the ignition,
but the engine is not
running, as a check to show
you it is working.

Voltmeter Gage

When the engine is running, the gage shows the
condition of the charging system. Readings between
the low and high warning zones indicate the normal
operating range.
When your engine is not
running, but the ignition
is on (in RUN), this gage
shows your battery's state
of charge in DC volts.