No i dont have a manual. I can drive on the highway no problem. I guess I'll head up to the shop today and see if the scanner can shift it. I did check the connector between the pcm and trans, it looked alright. No visible damage or anything. All fuses are good. If I can't figure this out by the weekend I think I'll just sell it as is. This will be my first and last cadillac that I own.

I've been out of pocket for a while, so I haven't been around. 3 different trannys doing the same thing eliminates the trans itself as the cause of the problem. What you have, from what I read here, is a PCM issue, or no power to the trans connector. You do need to find a way to scan for codes, either by using the on-board diagnostics, or by taking it to AutoZone, or some shop to scan for codes.

Can this be a similar issue:
My question if you have time to answer is this: I have a 1996 Seville SLS and my trans is not shifting to 3. It shifts from D! to D2 but D3 it spins like in neutral. If I manually place in D3 it moves but does not seem to D3 maybe D2. Could this be a solenoid? or clutches. I need some direction before I move forward. Additionally my ISS have been out for the last two years but has been driven with no apparent affect. This just recently started. Any thought?

You need to pull codes before figuring out where to go first. Codes will normally put you on the right track. A 1-2-neutral can certainly be a shift solenoid problem. It's possible that the trans is actually downshifting back into 1st gear, which at 30-40 mph would feel like neutral.
On most GMs 3rd gear is "failsafe", meaning if there is a problem that causes the power(voltage) to the trans to be shut down, it will have reverse and 3rd gears only....enough to get you home, or to a service center. See if unplugging the trans connector will still let the car move forward. If it takes off in 3rd gear, then you do most likely have a solenoid problem.
The shift solenoids are in the bottom pan, on the lower valve body, and it requires the valve body be removed, and dis-assembled to replace either of them.
If your ISS(input speed sensor) has been "out" for 2 years, I'd find it hard to believe that the trans is operating 100% properly. The PCM needs that signal to determine shift points, and gear ratios. Granted, it may be substituting the engine rpm/tach signal to operate the trans, but there's no way it could calculate the gear ratios in 3rd or 4th gear without a true input speed, since the torque converter causes a slight loss of speed/rpm until it goes into lock-up mode.

Get some code info, and post....let's see what we have to work with. :D

Thank you are your response. Besides the ISS (717 code) I have RS0036 for the road suspension. Yeah its hard to believe it drove without any effect. My thought it might be a false alarm....it occurs once the engine has warmed up. Also I did take the connector apart to clean and it appears to have transmission fluid in it...cannot see how it gets in there. Also had a water leak from the metal to rubber hose on the thermostat.
I will disconnect the trans connector and see if it will move forward. I finally got a diagram for the connector and will check the electrical readings for ISS and solenoids.
Once again thank you for your expertise...

Hometurf

Cadillac owner since '78

transmission code 717 ISS no signal
 

Will a lack of ISS signal cause the transmission to shift from 1 to 2 only.
After that it spins freely no torque but if I place in D3 it seems like D2.
I checked the resistance of ISS and it appears open.
Also there appears to be a fluid in the connector (dark pinkish like tranny fluid). I cleaned it out and it still comes out. Is this normal?

Adam Apple not sure if you are still around but I disconnected the connector and it drove so I do have 3rd gear. The fluid turned out to be engine oil coming from the leaking Oil sending unit nearby.
I still have the 717.
Do you know the symbol meaning when PCM? is displayed for a 1996 seville?
I have the transmission manual but it is for 2003 and the display is different.
When I drive I can see them coming on and off. It appears from my guesstimate that when it pcm initiates fourth gear ( i assume) it detects something is wrong and disengages the TCC...does that sound reasonable.
Thanks in advance for your technical assistance.

Hometurf