My first step would be to check the tone rings and wheel speed sensors
at each wheel.  (I ASSume that a 944 uses a 4-channel ABS system.  I
have a 944, but with no ABS, but I do have a decent working knowledge
of ABS systems, so I'm by necessity speaking in generalities.)

At each wheel you should see a tone ring somewhere in the hub
assembly, which looks like nothing more than a big open gear.  The
tone ring should be clean and free of gunk in the teeth, if one of
them is dirty the WSS will not pick up properly as it won't "see" the
"teeth."

If all the tone rings are clean, inspect the wiring coming from each
WSS.  if you see any obvious breaks, repair them (need to be very
particular here, solder your splices and use a little dab of
dielectric grease under the heat shrink - we're dealing with a very
low voltage signal here.)  If all the wiring is visually OK, jack the
car up, disconnect all the WSS's and connect a voltmeter set to AC
volts to the WSS wires.  When you spin each wheel, you should get a
low AC voltage at the corresponding WSS.  If one of them does not do
this, replace the WSS.  Also make sure the WSS is set at the specified
gap to the tone ring - too wide a gap will not allow it to work.

Anything beyond this is likely beyond the capabilities of the average
DIYer although I do not mean that to insult your intelligence - that
is about as far as I would feel comfortable going, myself.

Also, while you're messing with the brakes, now is a good time for me
to bring up one of my pet maintenance peeves, when was the last time
the brake fluid was changed in your car?  Don't forget to bleed some
out of the clutch cylinders as well.  Regular fluid changes are
important for long component life, especially so when you have ABS.
If you see gunk in the master cylinder reservoir remove it and clean
before bleeding; you do not want to be flushing crap through the ABS
unit, unless you like replacing expensive components.

good luck,

nate