BMW 318is Forum : “what could cause the abs light to stay on e36?”

It could be any number of things - from something as simple as a fuse to the ABS module or sensor itself.  

If you live in a cold climate where they use road salt, it is usually a sensor as they just corrode over time.

You're asking a very specific question without giving any specifics, however.  Have you done any brake work lately?  Have you modified the brake system in any way?  Has the vehicle been in a front end collision? What environment do you live in?  These are all things that have to be taken into consideration.....