[QUOTE=rjfjr1;1698475]Of the three sensors, the two-prong sensor is the one on the right (drivers side), there's a single-prong sensor on the left (which I replaced last night, we'll see if it makes a difference) and a four prong, circular sensor in the center. Haven't replaced the center sensor yet.[/QUOTE

Single wire sensor is the temp gauge sender unit.
The 4 wire is for CIS system
The one I posted is the aux fan high speed sensor. [ blu 2 wire picture]

If there is an open circuit on the sensor or the wires going to it, the ACC panel defaults into High Fan.
An easy test for this is to unplug the sensor and bridge the connectors wires with a 1K ohm resistor. If that shuts down fan, the sensor is faulty. If not, then pull the relay and see if fan stops.
Report findings.