IV. Background

During vehicle assembly Toyota uses brake fluids containing polymers that act as lubricants for certain brake system components. If replacement brake fluid is used that does not contain such polymers or contain only small amounts a part of the rubber seal (Brake Master Cylinder Cup) located at the rear of the brake master cylinder may become dry and the rubber seal may curl during movement of the piston. If this occurs a small amount of the brake fluid could slowly leak from the seal into the brake booster resulting in illumination of the brake warning lamp.


If the vehicle continues to be operated in this condition the brake pedal feel could change and braking performance could eventually begin to gradually degrade. If the warnings provided by the lamp illumination and the change in pedal feel are not heeded a vehicle crash could occur.


Toyota original brake fluid which is applied at the manufacturing plant contains polymers and does not cause this phenomenon.