Any 4T80E guru's on here??
 

I have a 2003 Cadillac STS Seville with the N*/4T80E trans in it. I've been having a nightmare of a problem that nobody, including myself, can seem to figure out. First, a little about the car. I recently purchased the car from my uncle who was having the same problem. The car only has 1st gear and won't shift out of it. He replaced the trans with one from the junkyard and still the same problem...only 1st gear. After dropping the pan and finding shavings EVERYWHERE he replaced the tranny again with another one from the junkyard. He tore it down, did a little overhaul on it and still the same problem....only 1st gear. He took it to a transmission shop that apparently found two of the wires leading to the trans to be bad: 1-2 shift solenoid and 2-3 shift solenoid wires were replaced from the PCM to the connector right before the wires go into the tranny. He got it back from the shop and everything shifted smoothly for a few days. Then back to the same problem. I bought it from him at this point. Me and my cousin both measured the resistance on the wires that were replaced and they were good. Now I've just recently replaced the 1-2,2-3 shift solenoid and installed the bracket kit along with some new fluid and filters. Drove it today and still the same problem. No change at all. I'm at wits end with this car. I love the car so I'd like to fix it. Here are the codes that keep coming up:

P1842- 1-2 shift solenoid circuit low voltage
P1845- 2-3 shift solenoid circuit low voltage
P1860- TCC PWM solenoid circuit electrical

After two transmissions and replacing the solenoids, these codes consistenly come back. At this point, I think it is a wiring/electrical issue but I just don't know enough about the car to figure it out. What do you guys think? Ever heard of a problem like this? Any help is appreciated and if anyone knows of any 4t80e guru's on here, please send them my way!! And maybe on the wild off chance....bad PCM???

One thing I forgot to mention...I don't know if this has any effect on it, but the gear selector on the DIC stays in park no matter what gear I'm in. The underline remains on P no matter where the shift lever is at. Maybe this is an issue?

PRNDL not working is a concern, no 12v to solenoids = 2nd gear only, check fuses. do you have manual or Alldata? Try to PM adams apple he's a trans guy

All fuses were checked and good. Thanks for the advice, I'll try to get a hold of him. How would I go about fixing the PRNDL on the DIC? I'm gonna bet that its a sensor inside the trans?

PRNDL switch is external, on trans beneath shift linkage

Thanks. I'll take a look tonight and let you know what I find.

I fixed PRNDL on the DIC. It was actually a slide switch inside the trans next to the valve body. Anyway, still the same problem. But we have made some progress. However, I don't know if this is good or bad. Now I can get the car to go into 2nd gear if I rev it up to about 45mph and let off the throttle. You can see the tach drop to 2k and when you give it throttle again, I'm able to get up to about 65mph before it is hitting 3.5k again. No gears after that, just 2nd. I'm stumped guys. Anybody have any sort of idea what is going on here? Maybe the TCC solenoid is stuck closed? Maybe a bad PCM still?

Do you have manual? Trans default is 2nd only so if you have 1st you have something. You need GM Tech2 to monitor data and manually try to shift trans. No codes swapping PCM is definitely worth trying. The problem could be with the car not the trans.

No, it is an automatic. I guess I'm not exactly sure what gears i have. All I know is I put it in D, get it to about 40mph, let off the throttle and it feels like it drops into the next gear. I can then speed up to about 65mph. It was only until recently that it started doing this. Before i only could go 40mph revving at 3k. All the same codes are still there. 2 shift solenoid codes and atcc solenoid code. I've tried numerous times to manually shift the trans, but with no avail. Are you saying try to shift the trans with the gm tech II? Where do i get one of these? I'm assuming the dealer...does anyone have an idea of how much they will charge to reprogram my PCM? I got a used one but have to get it flashed. And after that, I have to do a key relearn and a crank variance relearn as well? Thanks for all the help so far!

Manual meaning book or Alldata. Car will run highway speeds with only second gear. Dealer and maybe a repair shop have Tech2. You may have to take it to a shop. Check connector where it plugs into transmission and fuses. If a scanner will make it shift it could be PCM.

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