The brake light comes on but doesn't stay on. Is this because the fluid is low? How do I add brake fluid? How do I know how much to add? Is there a special kind to buy? 1997 Avalon

Use a Dot 3 conventional fluid and add to a clear plastic reservoir you will find under hood directlty in front of the steering wheel.There is a float inside which will detect low fluid and trip the indicator.Big concern is why is the brake fluid low in the first place?This will almost always mean wearing brake pad linings as the fluid will displace the missing lining thats worn off the pads.This probably is an indication that near future brake repairs are on the way which will include brake pad replacement. The other sitation you may enounter is once the pads are replaced,you will then be in an overfilled situation to where the fluid will have to be removed to have the correct amount. I would probably get a visual inspection on the brake lining wear then elect to add fluid at that time or replace brake pads.

Brake fluids for these cars are DOT3. You would know if you have the correct fluid level by looking at the break fluid container in the engine bay at the driver side. It has a cylindrical disc attached to the wall. It has the indicator to the level. It should be just at MAX. As for the light, check also if the fluid is dirty, it may need cleaning or the wires or the LED might be just loose.