An ABS warning light means the ABS system has been deactivated because of a self-diagnosed fault. Normal braking should remain. The vehicle should be safe to drive provided the driver does not have to call on his ABS system when panic braking on a wet or slick surface.
An ABS warning light may also indicate a loss of power-assist if the vehicle has an ABS system relying on an electric pump and pressure accumulator pump rather than a conventional vacuum booster. The car will still brake, but will not have the usual power assist. This could create an unsafe situation for drivers who have difficulty braking without power assist.
An anti-lock warning lamp that comes on when the car starts moving, or anti-lock braking operation or valve cycling that occurs during normal stops on dry pavement, often indicates a problem with one of the wheel speed sensors.
When both brake and antilock warning lights are on, and there is a lack of normal power assist, the pump may be inoperative on applications that have an integral ABS system.
When both warning lamps are on and power assist is present, it may indicate a low brake fluid level or loss of hydraulic pressure in one of the brake circuits.
ABS is essentially an add-on to the existing brake system. It only comes into play when traction conditions are marginal or during sudden panic stops. The rest of the time, it has no effect on normal driving or braking.
If brakes are pulling or grabbing during normal braking, it is not an ABS problem. The vehicle has a conventional brake problem needing attention.
A brake warning lamp (not ABS lamp) that remains on or comes on while driving, usually signals a problem with the hydraulic system, not the ABS system. There may be a fluid leak or loss of pressure, either of which pose a danger to safe braking. The cause of the brake warning light should be investigated immediately.