Volkswagen Repair: ABS light, obd scanner, speed sensors

Question
QUESTION: I have a 2002 Passat sedan and just got my rear brakes replaced in addition to replacing my two front drive shafts. As I pulled out of the garage (after writing a large check), I noticed my ABS warning light on (never on before).  It has been on for a few days now and my mechanic says that it will probably turn off in a few more days.  Should I be concerned?  Thank you.

ANSWER: Phoebe,
 I would be concerned.  If there was a minor, short term problem in the ABS, it should have cleared rather quickly, within minutes.  I would take it back soon before the shop can claim plausible deniability.  Besides, if it isn't a "real" problem, it only takes a few minutes for a qualified mechanic to hook up the OBD scanner and reset the error.  However, I believe when it is scanned, an error code will be discovered.  There are ABS sensors on each wheel, these are a vital part of what make the ABS function.  It is VERY plausible during any maintenance involving the wheels, that an ABS sensor could be inadvertently "bumped", i.e. disconnected or damaged.  Brake pad replacement is NOT equal to a preexisting ABS issue, so your mechanic is obligated to fix what did not exist before the car entered the shop.  The good news is it is probably an easy fix, like reconnecting a plug...hopefully.
-Rick

---------- FOLLOW-UP ----------

QUESTION: Thanks for your advice, Rick.  One more question-- So I took the car back and they took it to an get scanned and the problem that came up was with the speed sensor.  So the mechanic put in a whole new speed sensor, yet the ABS still comes up.  Reluctantly the mechanic re-scanned it and it reads that the problem is still the same.  Then he mentioned that it could be a problem with the new half-shaft that was installed.  He says that it's fine to drive in the meantime, and that he'll have time to look into it next week.  Should I go get a second opinion?  Thanks so much.

Answer
Phoebe,
  Keep in mind there should be 4 ABS speed sensors, but I am not absolutely sure for your model.  There would be one at each wheel, and any of these could be causing the same fault.   The most likely are one of the two fronts, but the one of the rear two could be suspect, perhaps a totally coincidental breakdown...or not?
- Rick