GMC Sierra Owners Manual
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.
There are only two reasons why the brake fluid level in the reservoir might go down:
• 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.
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.
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 5‑27.
Refer to the Maintenance Schedule to determine when to check the brake fluid. See Maintenance Schedule on page 11‑3.
Checking Brake Fluid
Check brake fluid by looking at the brake fluid reservoir. See Engine Compartment Overview on page 10‑6.
The fluid level should be above MIN. If it is not, have the brake hydraulic system checked to see if there is a leak.
After work is done on the brake hydraulic system, make sure the level is above the MIN but not over the MAX mark.
What to Add
Use only new DOT 3 brake fluid from a sealed container. See Recommended Fluids and Lubricants on page 11‑12.
Always clean the brake fluid reservoir cap and the area around the cap before removing it. This helps keep dirt from entering the reservoir.
With the wrong kind of fluid in the brake hydraulic system, the brakes might not work well. This could cause a crash. Always use the proper brake fluid.
• Using the wrong fluid can badly damage brake hydraulic system parts. For example, just a few drops of mineral-based oil, such as engine oil, in the brake hydraulic system can damage brake hydraulic system parts so badly that they will have to be replaced. Do not let someone put in the wrong kind of fluid.
• If brake fluid is spilled on the vehicle's painted surfaces, the paint finish can be damaged. Be careful not to spill brake fluid on the vehicle. If you do, wash it off immediately.