ABS power brakes can fail for a number of reasons. For example, a wheel rotation sensor can fail, causing the system to go into “fail safe” mode or “limp” mode. “Fail safe” mode means that the car’s brakes will work, but the anti-lock feature will not. You can determine that there is a problem with your brake system if the brake warning light comes on and remains on. ABS can fail because its computer or Electronic Control Unit (ECU) module has failed. If this happens, your car also enters “fail safe” mode. ABS systems can fail due to dust, moisture or hard use. If your brake warning light comes on, get your car to a technician as quickly as possible.
For more info, see How to Repair Power Brakes in 5 Steps