VSS and Transmission Output speed

[Peter D. Hipson]

I'm doing extensive work on the TISS/TOSS senders. No, they are not equal
in pulses per revolution, there is a substantial difference. (I've the
ratios, if that's important...) The senders are both magnetic coil type,
returning an A/C signal who's frequency (and voltage) varies with the RPM.
The only reason the voltage changes is due to improved efficiency at higher
speeds--the voltage change is not significant to the TCM, for example. Be
aware that common mode noise can be a problem with these senders, as can
bad connectors. As well, the sender itself fails frequently--arrggg! <g> 

At 11:01 PM 3/11/99 -0500, you wrote:
>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
>
>
>
Thanks, 
        Peter Hipson (founder, NEHOG)
        1995 White NA Hummer Wagon