GMC Yukon 2007 Owner's Manual page 490

So, it is not a good idea to top off your brake fluid.
Adding brake fluid will not correct a leak. If you
add fluid when your linings are worn, then you will
have too much fluid when you get new brake
linings. You should add or remove brake fluid, as
necessary, only when work is done on the
brake hydraulic system.
CAUTION:
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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.
When the brake fluid falls to a low level, the brake
warning light will come on. See Brake System
Warning Light on page 250.
490
Refer to the Maintenance Schedule to determine
when to check your brake fluid. See Scheduled
Maintenance on page 578.
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.
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.