I've been living without the VSS working for 5 years and I wanted to figure out what was wrong, so used this procedure to test it (but just with a voltmeter, not oscilloscope):

http://www.youtube.com/watch?v=WR_vdU1b1rs

Positive on top, negative, signal on bottom. I spun it and I only saw an increase of a half a volt on the signaling phase instead of 12. I have a used spare that I just got off ebay that claimed to be good and it acts exactly the same.

What am I missing here? Is my procedure wrong or am I just lucky enough to have two dead VSS units?

By the way, for some reason I had 12v at the ECM end of the harness for the VSS whether the vehicle was moving or not. I checked again with the cluster out and it's at 0. Continuity is good between the cluster connection and the ECM end of the harness.

 

Update: I probed every wire that has to do with the VSS on the cluster and on the main harness and everything seems fine, but what I don't understand is why I still have a constant 12V on the signal wire going to the ECM with the cluster installed. It seems like it should be the crappy 0 - 0.5v signal I get when I test the VSS on the bench.

I'm out of ideas for testing this besides buying a new optical VSS for almost $100.

 

Well, this seems to be the proper operation for the VSS. I have a wiring issue on the body wiring somewhere. I've bypassed the wiring with some test leads and I'm reading proper speed input on the scanner.