Normal Operation

It is important to know enough about the Anti Lock Brake
System (ABS) to be able to discuss with a customer what is considered normal operation of the system. The system comes into play only when a wheel begins to lock up. Under all other conditions the system is "transparent", i.e., the vehicle's brakes act as if there were no ABS. When the system senses that a wheel is about to lock up, then it begins to modulate the hydraulic pressure in the brake line to that wheel, allowing the wheel to continue turning. It does this in a pulsing manner, and this pulsation is transmitted to the brake pedal, and possibly the steering wheel as well. This is a normal operating characteristic of the system. Another characteristic of the system is a "whine" from the electric motor that drives the ABS. This sound is heard during each self test sequence and also when the system is in operation. This, too, is a normal operating characteristic of the system that occurs only when the ABS is doing its job of preventing wheel lock up.

Another normal operating condition occurs when the system conducts its self check. This is done the first time after starting the engine that the vehicle reaches a road speed of about 5 mph. A thump may be heard from the engine compartment, and if the brake pedal is depressed during the system check, a vibration may be felt as the pedal moves during the check. These are normal operating conditions.

The ABS warning light on the instrument panel has a normal cycle. When the ignition is turned on, the light illuminates. It normally stays on while the starter is operating, and after the engine starts the light goes off. If the light stays on, it signals a malfunction in the system. However, normal braking action is unaffected even with the ABS light on.