Now every Subaru sold since 2000 has been fitted with ABS, as part of the active safety package fitted to all Subarus.

Active safety is the collective term used to describe those components in a vehicle which are designed to avoid an accident, rather than protect the occupants once the crash has taken place.

ABS - or anti-lock or anti-skid - brakes as they are sometimes called have come a long way since they were first fitted to the Legacy.

Now more efficient and faster acting and more complicated as a result, the car's ABS system is also used for other electronic driver aids like the Vehicle Dynamic Control system which first appeared on the previous model Outback H6 in 2000.

But ABS's primary function has not changed. They are designed to prevent the wheels locking up in emergency stopping situations and provide the driver with more control over the car.
Initially ABS-equipped Subarus had three channel systems. A sensor on each hub detects when a wheel is locking up under braking load and the electronic control unit - a mini computer - then regulates the amount of brake hydraulic pressure being fed to a wheel.
Under the three channel system, the pressure supplied to each front wheel can be controlled independently, but if one back wheel locks up, the brake pressure to both rear wheels is reduced as there is only one channel to both rear wheels.

Now all Subarus have a four sensor, four channel system, so the braking on every wheel can be regulated independently of other wheels to get the maximum braking affect and the shortest stopping distance. The change to a four channel system came with 1995 model cars.

But ABS only works if you really slam on the brakes, as hard as you possibly can. Finesse is not a pre-requisite and just applying the brakes as you do in normal everyday driving won't produce the desired effect either.

A modern Subaru ABS system works about three times faster than in a Legacy equipped model of the early 90s.

Early ABS systems were known for the brake pedal pulsating under the driver's foot as the brakes were released and then reapplied continually as the wheels were about to lock up under each application of the brakes. A modern ABS system applies and then releases the brakes on the verge of lockup and then reapplies them about 50 times a second.

The Subaru ABS system is technically more advanced to those ABS systems fitted to two-wheel-drive cars because of the Subaru's All Wheel Drive transmission. With AWD, all the wheels are mechanically linked to one another through the driveshafts, differentials and transmission, so the rotational differences between the four wheels are more crucial to the operation of the ABS.

If one wheel is braked to a greater amount by the ABS than the other wheel on the same axle, then the ABS control unit has to electronically make adjustments so there is not any significant mechanical back lash through the drive shafts into the differentials and gearbox.
The ABS fitted to New Zealand and Australian Subarus is also different from that in European, American or Japanese market bound cars. The ABS for Kiwi Subarus has been tuned to react better on our loose-surfaced, backcountry gravel roads, so it will bite through the loose metal onto the harder road surface underneath.

The ABS sensors - one on each wheel - are also the cornerstone of the Vehicle Dynamic Control system, which applies brakes on each corner of the car totally independently to lessen oversteer or understeer in corners. Oversteer is when the rear of the car slides out of line, while understeer occurs when the front of the car wants to keep pushing straight ahead, even while the driver is trying to turn into and steer through a corner.

All ABS systems have a self diagnosis system. When you first turn on the ignition, the ABS warning light will come on as the system checks itself. Once the light goes out you know the ABS is fully operational. If there is a problem the light will stay on..! The braking system will still work, without all the ABS benefits, so it will need to be fixed by an authorised Subaru workshop straight away.

Those hub sensors also aid the EBD or electronic brake force distribution fitted to some models. Standard ABS just applies the brakes to the verge of lock-up, with equal force to all wheels, but EBD applies varying amounts of force to maximise the braking.

But the biggest thing to remember with ABS is to make the best use of it in emergency situations. There have been numerous examples of drivers using the ABS in an accident, but still hitting the object they were trying to avoid. Yes, the wheels did not lock up, but the driver forgot the car had the ability to steer while the ABS was braking the wheels to maximum affect.

A vehicle without ABS loses all steering control once the front wheels are locked up under emergency braking and the vehicle just ploughs straight into whatever happens to be in its path. But using ABS to its best advantage allows you to brake as hard as possible, without wheel lockup and then steer around whatever might be in your way, while still braking as hard as possible.

You hope you never have to put ABS to the ultimate test, but it is nice to know what it can do if required.