You can't read ABS diagnostic codes on a 240. Does your ABS system deploy unexpectedly, or is it just that the ABS light is on? If the former, this might apply:

The ABS on my 93 acted up a while back. When I would come to a slow stop, the ABS would deploy right before the car stopped. The problem turned out to be a worn tie rod that allowed the wheel to wiggle a bit, just enough that the ABS system interpreted it as wheel spin. I replaced the tie rod and the problem was solved. It surprised me because the amount of play was very small. Cleaning the sensor could also help, but to do a really got job, remove the rotor and clean the reluctor (toothed) wheel on the back.

If the ABS is not deploying but the light is always on, check the fuse. The ABS computer is under the passenger seat near the front (moved from earlier years). You have to take out the seat and pull back the carpet to get to it. There is a fuse in the front of the unit. Make sure that fuse is not blown. FYI, removing this fuse will cause the ABS system to be inactive, but the light will stay on.

Let us know how you finally fixed it.