2012 GMC Sierra Owner's Manual - Page 414

10-28 Vehicle Care There are only two reasons why the brake fluid level in the reservoir might go down: . If this is not done, the brakes might not work properly. For example, installing disc brake pads that are wrong for the vehicle, can change the balance between the front and rear brakes - for the worse. The braking performance expected can change in many other ways if the wrong replacement brake parts are installed. { WARNING If too much brake fluid is added, it can spill on the engine and burn, if the engine is hot enough. You or others could be burned, and the 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 comes on. See Brake System Warning Light on page 5‑25. Refer to the Maintenance Schedule to determine when to check the brake fluid. See Maintenance Schedule on page 11‑3. The brake fluid level goes down because of normal brake lining wear. When new linings are installed, the fluid level goes back up. A fluid leak in the brake hydraulic system can also cause a low fluid level. Have the brake hydraulic system fixed, since a leak means that sooner or later the brakes will not work well. . Brake Fluid The brake master cylinder reservoir is filled with DOT 3 brake fluid. See Engine Compartment Overview on page 10‑6 for the location of the reservoir. Do not top off the brake fluid. Adding fluid does 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.