GMC Cadillac CTS 2004 Owner's Manual page 163

Charging System Light
If this light stays on, your vehicle needs service. You
should take your vehicle to the dealer at once. To save
your battery until you get there, turn off all accessories.
For more information see DIC Warnings and Messages
on page 3-70.
When you turn the key to
ON or START, this light will
come on briefly to show
that the generator and
battery charging systems
are working properly.
Brake System Warning Light
Your vehicle's hydraulic brake system is divided into two
parts. If one part isn't working, the other part can still
work and stop you. For good braking, though, you need
both parts working well.
If the warning light comes on, there is a brake problem.
Have your brake system inspected right away.
United States
This light should come on briefly when you turn the
ignition key to ON. If it doesn't come on then, have it
fixed so it will be ready to warn you if there's a problem.
Canada
3-43