GMC 2010 Sierra Owner's Manual page 506

Checking Brake Fluid
Check brake fluid by looking at the brake fluid reservoir.
See Engine Compartment Overview on page 6 16.
After work is done on the brake hydraulic system, make
sure the level is above the MIN but not over the
MAX mark.
What to Add
Use only new DOT 3 brake fluid from a sealed
container. See Recommended Fluids and Lubricants on
page 7 13.
6-46
The fluid level should be
above MIN. If it is not,
have the brake hydraulic
system checked to see if
there is a leak.
Always clean the brake fluid reservoir cap and the area
around the cap before removing it. This helps keep dirt
from entering the reservoir.
WARNING:
With the wrong kind of fluid in the brake hydraulic
system, the brakes might not work well. This could
cause a crash. Always use the proper brake fluid.
Notice:
Using the wrong fluid can badly damage
brake hydraulic system parts. For example,
just a few drops of mineral-based oil, such
as engine oil, in the brake hydraulic system
can damage brake hydraulic system parts
so badly that they will have to be replaced.
Do not let someone put in the wrong kind of
fluid.
If brake fluid is spilled on the vehicle's
painted surfaces, the paint finish can be
damaged. Be careful not to spill brake fluid
on the vehicle. If you do, wash it off
immediately. See Washing Your Vehicle on
page 6 124.