The 01 ABC system has had a few issues. However, 3 issues stand out and are rather inexpensively addressed.
1)Rear line worn through- There is a fluid line inside the rear wheel well. Easily seen if tire is removed. Clearance with tire is VERY close if car is fully loaded / over loaded. Check for wet areas. Change out with used line is cheapest ... $100+
2)Bent Rear Sensor Mount - If car has hit a "pothole" or large bump while fully loaded / over loaded, the rear frame will bottom out directly onto the rear sensor and bend the tab downward. This can be seen easily by removing the rear wheel(s). The vehicle "thinks" it is in a much different position then it really is and continually attempts to correct. Locate it. Compare with other side (hopefully not bent also) or, a car you know is working. Correct the ahgle of the tab with needle nose pliers and problem should end.
3) Combo PS and ABC pump is broken. This pump is on the drivers side, just behind radiator, a little under the coil bank. Check for whining noise, dampness, crack, leak, bad seal, loose belt. The pump may be replaced with a remanufactured, guarenteed pump for about $600, or ... Is you fluid level up ??? Be CERTAIN to use SYNTHETIC fluids in this car. If not you WILL destroy it.
4) Is your ABC system bled??? Simple to check on a lift.