1996 GMC Yukon Owner's Manual - Page 285

Brakes Brake Fluid Your brake master cylinder reservoir is here. I t is filled with DOT-3 brake fluid. So, it isn't a goodidea to "top off" your brake fluid. Adding brake fluid won't correct a leak. If you add fluid when your linings are worn, then you'll 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. If you havetoo 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 is fluid only when work done on the brake hydraulic system. There are only two reasons why the brake fluid levelin the reservoir might go down. The firstis that the bmke fluid goes down to an acceptable level during normal brake lining wear. When new linings are put in, the fluid level is goes back up. The other reason is that fluid leaking out of the brake system. If it is, you should have your brake system fixed, since a leak means that sooner or later your brakes won't work well,or won't work at all. Refer to the Maintenance Schedule to determine when to check your brake fluid. See "Periodic Maintenance Inspections'' in the Index. 6-31