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.