The action is necessary as a small amount of the brake fluid could leak from the brake master cylinder, leading to the illumination of the brake warning lamp.
“The Toyota genuine brake fluid used during vehicle assembly for vehicles sold in the United States contains polymers. The polymers act as lubricants for certain brake system components. If during vehicle maintenance, brake fluid is used that does not contain such polymers or only small amounts, a part of the internal rubber seal (brake master cylinder cup) located at the end of the brake master cylinder piston may become dry and may curl during movement of the piston. If this occurs, a small amount of the brake fluid could slowly leak from the brake master cylinder into the brake booster, resulting in illumination of the brake warning lamp,” explained the press release.
If the driver ignores the brake warning lamp and continues operating the vehicle without refilling the master cylinder brake fluid reservoir, the brake pedal will eventually offer a spongy or soft feel and the braking performance may gradually decline.
Toyota will notify owners of the involved vehicles via first class mail early next month. Owners will be asked to visit the dealers, where the brake master cylinder cup will be replaced with one that uses a new design. The operation will be performed free of charge.
Update: the recall affects a total of 1.53 million vehicles worldwide.