if its happening on snow/ice its normal (not very good in these conditions) in fact useless,

if ABS light is on all the time there is a fault and the unit is shut down,
if the light goes off after 3 seconds and stays off there is no problem,

 

Have you found what was causing the problem? I am having the exact same problem on my 98 A4 2.8Q stick ~87K miles.

I'm having an intermittent (80% of the time) problem with my ABS pulsing at slow speeds 2mph to 20mph on dry paved roads and light braking. No ABS indicator light on the dash at all, so nothing wrong with the ABS module it seems.

And how do we check whether the ABS sensor has been installed properly?

 

Get the car VAGed. Have the wheel speeds read.

https://www.audiforums.com/m_99381/tm.htm

 

as a general rule, under hard braking, it's teh rears that get all "anti-lock" first. Mostly because they're allways light;y loaded under heavy braking, and so more prone to setting off teh sensors. Cars being sorta like Women, in many regards, your ABS may be feeling neglected[&:]. *I* recommend taking it out and "reminding" the ABS what it's there for, 2, 3, 5 times, in a row. And I mean STOMP-ON-'EM-type reminder. if you can find some *moist* pavement, all teh better, if not... check your mirror brfore applying this technique. If THAT don't work, it's possible I don't know WTF I'm talking about...[8D]

 

Sounds like you have a dirty/damaged/corroded toner ring at one of the four corners. You may want to try removeing the sensors and taking a peek at the toner ring. You can also try sparying some brake clean in there to clean the ring.

 

I finally got it fixed. It was a cracked toner ring. Got the car VAG'ed.