Brake System Warning Light - GMC Sierra 2008 Owner's Manual

Readings outside the normal operating range may also
occur when a large number of electrical accessories are
operating in the vehicle and the engine is left idling for
an extended period. This condition is normal since the
charging system is not able to provide full power at
engine idle. As engine speeds are increased, this
condition should correct itself as higher engine speeds
allow the charging system to create maximum power.
You can only drive for a short time with the readings
outside the normal operating range. If you must drive,
turn off all unnecessary accessories.
Readings outside the normal operating range indicate
a possible problem in the electrical system. Have
the vehicle serviced as soon as possible.

Brake System Warning Light

With the ignition on, the brake system warning light will
come on when you set the parking brake. If you try to
drive with the parking brake engaged, a chime will sound
when the vehicle speed is greater than 5 mph (8 km/h).
Your vehicle's hydraulic brake system is divided into
two parts. If one part is not 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 and a chime sounds there
could be a brake problem. Have your brake system
inspected right away.
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