[Smith1000]

I tested the VSS on my '97 Lesabre years ago. You can do it with a digital voltmeter as well. The VSS, from what I recall, has a magnetic tip that generates its own voltage within a certain range. The voltage is variable with speed and provides an input for the ECU. The ECU then provides the signal to the dash gauge. I want to say the range is 0 to 1 volt (not exactly sure, it may be less than that). Regardelss, if voltage is being produced, and you can see it move from 0, then the VSS is doing its job and the speedometer should be producing some reading.

I tapped into the signal wire with a straight pin and an alligator clip. I taped the volt meter to the winshield (outside), so that I could read it through the windshield. You then have to drive around and watch the output.

If it is producing voltage, next the voltage can be checked going in and out of the ECU. Also, it could be checked at the gauge as an input. This rules out a problem at the ESU or with the wiring. That part is likely okay. It may just be in the cluster. For my 97, the speed was reading erratic. Also, the tach was jumping. It had a bad cluster. I found a salvaged one and that did the job. Good luck.