Up for sale is a Saab classic 900 used - good working condition Saab 900 ABS Electronic unit ECU.  Check your Original ATE part number to know which unit to buy. 4002176 is this unit,  This is located under your cars rear seat.

These units are quite reliable, however they are not water resistant.  I have seen failures due to corrosion in the past,  Aside from a physical failure, the only proper way to diagnose problems with this unit other than "guess and check" is with the Saab i-sat scan tool.   This unit was from a car with no ABS lights, and FUNCTIONS.  We will not accept returns on this due to a high misdiagnosis rate on these control units!  be sure it is actually your problem.