VSS and Transmission Output speed

[Shannen Durphey]

Hi, Dr. Plecan.

4L80E trans has 2 speed sensors installed, Transmission Input Shaft
Speed and Transmission Output Shaft Speed.  Early 4wd (pre94) had
separate VSS and dedicated signal to PCM, 2wd and 94+4wd didn't have
extra sensor so combined the signals.

TOSS is used for gear ratio calculations, VSS is used for shift
control.  TISS is used for TCC control, shift pattern, shift quality.

I remember a few codes for these, trans component slipping, tcc apply
error, undefined gear ratio, excessive shift times. 

Nothing I have gives # of pulses/rev, but I think the frequency is
different between the two shafts, due to different "wheel" diameters.
Definitely A/C from the sensor, as they are the same part no.  TISS
must be conditioned inside the PCM, TOSS may depend on the year of the
calibration.  Kinda makes the electronic
simulations a job for the entire CSH staff...
Shannen

Bruce Plecan wrote:
> 
> On a 8625 pcm, there are two connections, one labeled VSS, which is vehicle
> speed sensor, and a second one labeled transmission output speed,   they
> both feed from the Vehicle Speed Signal Bufffer to the PCM.  Can anyone
> splain this to me?.  Is this just a way of checking for transmission
> "slippage".
> Anyone happen to know what this 5v signal should be?.  ie square, 4,000ppm?.
> Thanks
> Bruce