Just the switch missing would set a code for the switch only.
Hard to troubleshoot without the exact code numbers otherwise.
Speculation; well; shorted sensor especially on the common could cause voltage readings to go nuts in the control module.
Really you need to look at all the sensor data on a scanner, see what you have. If you have low or out of range voltage all over the place, first step is to unplug each sensor and see if voltages return to normal on the others. If you unplug one, and other voltages return to normal; you know you have an issue in that sensor; same scenario for the wiring harnesses etc; but its hard to believe there is an issue there without mice, accident damage, corrosion;etc; that is unlikely. More so a sensor. This task is not possible without a scanner. Unless you just want to throw parts at it.
One thing you could do without a scanner, pull the sensors; look for obvious damage on the sensors, and excessive rust or damage on the tone rings. Check the wiring harnesses for damage/corrosion.
It is rare on these cars for there to be any trouble with an ABS module; of course; the newest one is now nearly 15 years old, so that statement could be null now; but I've never seen a bad ABS module on one of these; sensors; yes.