The definitive way is to connect an oscilloscope across the speed sensor output/input, at various points in the wiring, drive the car and look at the wave form.
Assuming that you don't have one of those
)), a DMM with a frequency function can be used instead - ~$40 will get something suitable.
Auto. or manual?
If it's auto., that's an inductive pick up type so it's an AC voltage output - maybe ~1V - and both the frequency and voltage of the sensor output should change (increase) with road speed. Measure it across the two wires out of the sensor. It will probably be easiest to do that at the PCM. Backprobe - use dressmaker's pins carefully inserted in between the back of the wire terminals and plastic connector body to access the wires.
Rob's Creative Calibrations (search) should have the wiring diagrams. V6 VT and VS are virtually the same at the PCM if one or the other diagram isn't clear.
You can also check the resistance of the wire coil - I don't know what it should be but it shouldn't be open circuit and you can compare it to the old sensor.
The other component of the sensor is a toothed wheel (maybe that's the "gear"?) that rotates past the coil and magnet. You can inspect that visually with the sensor removed, looking for broken or bent teeth. Usually that's OK though.
The distance between the sensor magnet and the teeth is important so if there is something that is preventing the sensor from sitting properly that can affect it's operation.
You should also check that the wires between the sensor and PCM aren't broken - DMM on lowest "Ohms" setting. Yes, it's OK to swap/solder the wires if they do come up as broken.
