[A4] ABS problem

[Peter Kirby]

The ABS on my 2001 1.8tq is acting up.  As I am braking, once I hit
around 20 km/h I start getting a few pulsations from the ABS.  It
started out with just a couple of pulsations/stop but now there can be
many more.  The ABS light does not come on (but does come on at
startup and then goes off right away, as it should).   A friend
claimed he had similar symptoms on his 1997 1.8 tq and it turned out
to be broken ABS rings on the rear CV joints.  On the old 20v.org site
they indicate that similar symptoms are seen when a wheel sensor is
flakey or too far away from the rotor.

However, when I hook up either my Prodiag or my local garage's VAGCOM,
we can only maintain communication with the ABS ECU for a short period
of time before the connection is broken.  While connected, the four
wheels are shown as turning equally (both the Prodiag and VAGCOM give
simultaneous wheel speed outputs).  My garage person feels that the
ABS module is not good and that needs repair/replacement (I see there
are a few places on the web that do this).

Any thoughts?  Any other diagnostic tests I can do to narrow down the
possibilities?  I am reluctant to start pulling off the half-shafts to
find out which one(s) might be the problem.

Thanks.

Peter