Hummer 2007 H2 Owner's Manual page 428

Checking Brake Fluid
You can check the brake fluid without taking off
the cap.
After work is done on the brake hydraulic system,
make sure the level is above the MIN but not
over the MAX mark.
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Look at the brake fluid
reservoir. The fluid level
should be above MIN.
If it is not, have your
brake system checked to
see if there is a leak.
What to Add
When you do need brake fluid, use only DOT-3
brake fluid. Use new brake fluid from a sealed
container only. See Recommended Fluids
and Lubricants on page 528.
Always clean the brake fluid reservoir cap and the
area around the cap before removing it. This will
help keep dirt from entering the reservoir.
CAUTION:
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With the wrong kind of fluid in the brake
system, the brakes may not work well, or
they may not even work at all. This could
cause a crash. Always use the proper
brake fluid.