The brake master cylinder reservoir is filled with GM approved DOT 4 brake fluid as indicated on the reservoir cap.
Checking Brake Fluid
With the vehicle in P (Park) on a level surface, the brake fluid level should be between the minimum and maximum marks on the brake fluid reservoir.
There are only two reasons why the brake fluid level in the reservoir may go down:
With a leak, the brakes will not work well.
Always clean the brake fluid reservoir cap and the area around the cap before removing it.
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 fluid, as necessary, only when work is done on the brake hydraulic system.
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.
When the brake fluid falls to a low level, the brake warning light comes on. Brake fluid absorbs water over time which degrades the effectiveness of the brake fluid. Replace brake fluid at the specified intervals to prevent increased stopping distance.
What to Add
Use only GM approved DOT 4 brake fluid from a clean, sealed container.
Warning: The wrong or contaminated brake fluid could result in damage to the brake system. This could result in the loss of braking leading to a possible injury. Always use the proper GM approved brake fluid.
Caution: If brake fluid is spilled on the vehicle's painted surfaces, the paint finish can be damaged.
Immediately wash off any painted surface.