[V6-12v] ABS

[Tom Christiansen]

At 06:59 PM 3/1/2005, Clive Young wrote:
>Hi Guys
>
>I was out on the snow the other day  ( in my luke warm audi :-)  ) and 
>realized my ABS may not be working at all. Locked up the wheels. several 
>times on ice, no kick back on the pedal at all. anyone know a sure fire 
>way to check ?

Does the ABS light come on during start-up? If not, check the bulb.

If the ABS light does come on during start-up, but then turns off (like it 
should), it's a more serious problem. I would suspect a faulty ABS 
controller. The reason I'm opting for the most expensive part by default is 
that the ABS controller is supposed to perform a partial self-check when 
you start the car. During this self-check, the ABS light is on. If no 
faults are found, the light goes out. But the test is only partial as the 
controller can't test the operation of the ABS control valves, return pump, 
or the wheel speed sensors. At least I don't think it can test the valves, 
pump. I'm positive about it not being able to test the sensors. Thus, if 
the system finds a fault during operation it'll turn on the light and turn 
itself off.
There's supposed to be a couple of relays in the ABS unit under the hood. 
Those are the only parts that you are allowed to replace. There's also a 
fuse somewhere...

Above is based on my ABS manual for the 5000. I don't think the concept has 
changed much since then, although, obviously, the technology has improved 
and parts have been redesigned for better performance. But the overall 
system works roughly the same. - Obviously, the manual requires you to have 
the Magic VW1234 tester specifically for testing the ABS unit.

TOm