I had this problem with the ABS twice on my '98... once for the front right wheel, then later for the left. I needed new hubs. The hubs didn't have wobble or make noise yet but apparently either bearing wear changed the spacing or what i suspect was the grease inside was contaminated with metal particles and got on the sensor reluctor (aka tone ring) teeth (in the hub, since mine has 4WD) to drop signal strength.
The first time I just replaced the sensor (and used a paint brush to fling some grease out of the tone ring teeth) and it went away for a month then came back, so replaced the hub. Next time on the other front wheel, just replaced the hub. Hubs "usually" come with a new sensor.
I did check the old sensors, which were intact including getting a resistance measurement around 420 ohms. Well they were intact besides the fact that trying to remove them, ripped the plastic shell off the sensor but the coil inside was still good and give the same 420 ohms.
Sometimes, as with my case, you can tell whether it is a front sensor and which one, by letting go of the steering wheel when coming to a ~ 5MPH stop. If the vehicle pulls to the side, it is the opposite side front sensor signal that's lost. IE - if it pulls left, it's the right sensor signal missing.
You stated no pulling or pulsating though, so it might not be a front sensor, or even ABS at all. I forget the ohm value of the rear sensor but you can try measuring it at the ABS controller connector. I think it should be very roughly 150 ohms (or maybe it's higher, I just remember there were a few hundred ohms difference between the front and rear), just not open circuit or short circuit. This connector is a little tricky to get off the ABS module, you have to grab the part pictured on the left, and slide it upwards (or sideways on my sideways picture!) to unlatch the connector. Pay no attention to the ABS module part #, this pic might have come from an F150 pickup truck instead of an Explorer.
