1999 GMC Sonoma Owner's Manual - Page 271

yellowblue NOTICE: D Using the wrong fluid can badly damage brake system parts. For example, just a few drops of mineral-based oil, such as engine oil, in your brake system can damage brake system parts so badly that they'll have to be replaced. Don't let someone put in the wrong kind of fluid. If you spill brake fluid on your vehicle's painted surfaces, the paint finish can be damaged. Be careful not to spill brake fluid on your vehicle. If you do, wash it off immediately. See "Appearance Care" in the Index. Brake Wear If you have four-wheel drive, your vehicle has four-wheel disc brakes. If not, your vehicle has front disc brakes and rear drum brakes. Disc brake pads have built-in wear indicators that make a high-pitched warning sound when the brake pads are worn and new pads are needed. The sound may come and go or be heard all the time your vehicle is moving (except when you are pushing on the brake pedal firmly). D CAUTION: The brake wear warning sound means that soon your brakes won't work well. That could lead to an accident. When you hear the brake wear warning sound, have your vehicle serviced. NOTICE: Continuing to drive with worn-out brake pads could result in costly brake repair. 6-33