GMC 2009 Sierra - Manual (Page 348)

Brakes
Brake Fluid
The brake master cylinder
reservoir is filled with
DOT-3 brake fluid. See
Engine Compartment
Overview on page 5-12
for the location of the
reservoir.
There are only two reasons why the brake fluid level
in the reservoir might go down. The first is that the brake
fluid goes down to an acceptable level during normal
brake lining wear. When new linings are put in, the fluid
level goes back up. The other reason is that fluid is
leaking out of the brake hydraulic system. If it is, you
should have the brake hydraulic system fixed, since
a leak means that sooner or later the brakes will
not work well.
It is not a good idea to top off the brake fluid. Adding
brake fluid will not correct a leak. If fluid is added
when the linings are worn, there will be too much fluid
when new brake linings are installed. Add or remove
brake fluid, as necessary, only when work is done on
the brake hydraulic system.
{ CAUTION:
If you have too much brake fluid, it can spill on
the engine. The fluid will burn if the engine is
hot enough. You or others could be burned,
and your vehicle could be damaged. Add brake
fluid only when work is done on the brake
hydraulic system. See “Checking Brake Fluid”
in this section.
Refer to the Maintenance Schedule to determine when
to check the brake fluid. See Scheduled Maintenance
on page 6-4.
5-36