2009 GMC Sierra 1500 Crew Cab Owner's Manual - Page 452

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. Checking Brake Fluid Check brake fluid by looking at the brake fluid reservoir. See Engine Compartment Overview on page 5-16. The fluid level should be above MIN. If it is not, have the brake hydraulic system checked to see if there is a leak. { CAUTION: 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. Refer to the Maintenance Schedule to determine when to check the brake fluid. See Scheduled Maintenance (Gasoline Engine) on page 6-4. After work is done on the brake hydraulic system, make sure the level is above the MIN but not over the MAX mark. 5-42