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Hotrodders.com Moderator
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Discussion Starter · #1 ·
Does anyone know the proper way to test a magnetic VSS on a 99 2500 Chevy truck?.

I have checked continuity through the wiring to the ECM (Good), and put an ohm meter to the VSS, and passed metal in front of it, and the resistance varies. How much resistance should it have if it's stationary?.

The truck has no speedometer, throws a code for lack of VSS signal, but I think maybe the VSS is okay, as well as the wiring.

This is causing shifting problems with the 4L80E transmission.

I'll post this in the trans section too.

Any help will be appreciated.

Brian
 

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Bowtie or Die!
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636 Posts
I don not have the specs but the VSS produces a A/C signal. Get an A/C meter or multi meter put it on the sensor and run the truck in gear off the ground and check a/c voltage you should see a signal that will change with output shaft speed.
 

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Administrator
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usually when a speed-O quits functioning in late model stuff.... it is the VSS.

Sometimes gunk covers them up and causes erratic readings
 

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when will it rain???
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1,295 Posts
what u need is an output speed sensor that goes on the case, not the one on the differential. that should fix u right up...
btw its on left side, just above the big round connector near the back of the case. itll be a 2 prong plug. :thumbup:
 

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when will it rain???
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1,295 Posts
dont have to. common mistake made with getting vss code when dealing with a 4L80E. they have input and output turbine sensors of left side of the case and when faulty, can throw a vss code... most who dont know about the workings of the 4L80E will usually go to the old stock bullet location and notice they didnt put it there anymore, and get misguided info at times about the vss on the diff... probably had a dozen or so trucks come in because of this exact issue in this past year alone. as far as what i said b4, my call still stands, but also something to keep in mind with those units, a faulty PRNDL switch can cause erratic shifts, and so can a wet pass-through connector, but neither will have an effect on speedo... output speed sensor will...
 
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