Shuddering transmission harsh shifts p1811 p1639 99 venture poor performance

I have been experiencing the harsh shifting, shift delays and shuddering described in many posts regarding this tranny. I took the van into a couple of tranny places and most said rebuild. One told me "oh, P1811? that means we have to rebuild the tranny, its gonna cost about $3k." A lot of these tranny places pretend they have never heard of a problem with these transmissions? Anyway, This forum is great for arming a customer with information to prevent getting ripped off. but now onto the problems I have been having, maybe someone can help. The vehicle's mileage has been getting worse, and the shuttering seems to be a little worse. The harsh shifting is frequent but no more than before and it comes and goes. I had never had the check engine light on before even though P1811 was present, however the light came on today. The two codes that came up were P1811 "Max adapt" and P1639 which from what I have found is "5 volt reference 2 circuit" Does anybody think that these two codes are related? I bought some stuff to clean the MAF but haven't done so yet. I have read some posts that say replace the PCS which is what I am leaning toward doing but I know it will be expensive and my faith in the tranny places I have been is very low. I have lost my train of thought....HELP!!!

I also forgot to mention that there is no burnt smell to the tranny fluid and it is pink(ish)....I had the filter and fluid changed, not flushed and there were no metal shavings or debris....the problem doesn't seem to be related to temperature and seems to be related more to driving time at highway speeds althogh sometimes jerks right from cold start. I am at a loss....I do not trust any of the shops I have been to...

I can't find a reference to the P1811 DTC in my 98 shop manual. Either something's funky somewhere, or that is a newer error code that was added in a subsequent year from mine.

The P1639 DTC is indeed the 5V reference circuit. That 5 volt line is used for the AC Refridgerent pressure sensor and the fuel tank pressure sensor. This DTC will NOT set the MIL so the 1811 error code was what set it on. The diagnostic procedure basically says to check wires, harnesses, and ground points. If those are all good, then replace the PCM but I would say that would be as a last resort. It could also have been a 1-time hiccup.

Know this is an old post, but thought I'd throw in my 2 cents... As far as I understand, the Max Adapt code means that the control module has attempted to adjust the line pressure (in order to get the appropriate amount of slippage during a shift) by as much as it can. I think these vans have the GM 4T65E transmission which up until MY2003 used a Delphi pressure control solenoid. These things are not the best... they have a rather weak design in that the armature wears quickly against its bearing and the pressure regulation becomes imprecise. I actually just had to change the same part on my 2002 Saturn L100 (4T40E transmission, but same electronic components) for similar symptoms (harsh shifts and shuddering). I tore mine down to analyze the part and the wear on the armature was quite deep. Good news is you can get a replacement PCS for less than $40. Bad news is they are a bit of a pain to get to on the front drive transmissions (took me about 6 hours to replace one, but could probably do it in about 4 if I had to again).

Know this is an old post, but thought I'd throw in my 2 cents... As far as I understand, the Max Adapt code means that the control module has attempted to adjust the line pressure (in order to get the appropriate amount of slippage during a shift) by as much as it can. I think these vans have the GM 4T65E transmission which up until MY2003 used a Delphi pressure control solenoid. These things are not the best... they have a rather weak design in that the armature wears quickly against its bearing and the pressure regulation becomes imprecise. I actually just had to change the same part on my 2002 Saturn L100 (4T40E transmission, but same electronic components) for similar symptoms (harsh shifts and shuddering). I tore mine down to analyze the part and the wear on the armature was quite deep. Good news is you can get a replacement PCS for less than $40. Bad news is they are a bit of a pain to get to on the front drive transmissions (took me about 6 hours to replace one, but could probably do it in about 4 if I had to again).
Albert, could the "PCS" be causing my 2001 to no longer shift into overdrive(4th)? Seems at around 80-90 KPH(50 MPH) I hear a whinning noise but feels like van is staying in 3rd... Also does the tranny have to be rebuilt or just a partial dis-assembly?

Thanks!

Albert, could the "PCS" be causing my 2001 to no longer shift into overdrive(4th)? Seems at around 80-90 KPH(50 MPH) I hear a whinning noise but feels like van is staying in 3rd... Also does the tranny have to be rebuilt or just a partial dis-assembly?

Thanks!

If the PCS output pressure were low to the point of causing unacceptable slippage, then the control module would command max pressure and inhibit torque converter lockup to protect the transmission. This might feel like no fourth gear, but it would accompanied by a check engine light and hard shifts into 2nd and 3rd. Except for that, I don't think the PCS itself would cause anything that feels like a no 4th condition.

If you're asking whether or not it is necessary to rebuild a transmission to replace the PCS, then the answer is no... just a good bit of work to get the side cover off for access to the solenoids. Some of the mechanical issues that would cause a loss of 4th might justify a complete rebuild though.

Hope this helps.

I had a 2000 Venture with the P1811. It had harsh shifts after it warmed up. I was going to replace the pressure control solenoid, but decided to try solution-in-a-bottle first. I used Seafoam TransTune and IT WORKED! Ten miles after pouring in the Seafoam I changed the fluid and the problem went away. Woo hoo!!