'92 100CS FWD AT - Transmission Troubleshooting BTDT

[urq]

My nephew asked me if I could help h was having with his ’92 100CS FWD with
automatic (12vV6) 
 the transmission appears to slip in one gear in mid
range.  We took it for a test drive, it appears that 3rd gear is slipping.
This test drive also warmed up the engine and tranny fluid, so we checked
the level afterward.  It looked like the fluid level was low, so we added
some ATF 
 no change to the symptoms.  We drove back to my house so we could
see if ProDiag could find anything 
 I was able to communicate with the
engine and climate control, but nothing with the transmission (I used the
’92 100CS entry in ProDiag).  

 

So 
 has anyone ever used ProDiag to talk to a tranny controller on a car
like this?  

 

Anyone have similar problems happen on their car?  I’ve got almost no
experience with automatics 
 but I’m thinking there may be some sort of
electronically controlled valve that is not working.  Any assistance greatly
appreciated!

 

The basic symptom is that the car will accelerate to around 40MPH, at which
time the transmission slips, so that the engine will rev freely with
throttle application.  There’s enough coupling for the car to accelerate
slightly to the point where the transmission will shift to the next gear 

at which point the car runs as expected 
 until you slow down to the point
where you have to accelerate through 40MPH again.

 

Steve B

San José, CA (USA)