2000 Pontiac Montana transmission issues

[Slicer89]

We have a 2000 Pontiac Montana that has 235k on the clock - Unsure of how well the transmission was taken care of, but it seems to fine as of late.

Now it seems to be shifting hard, checked fluid, was a little low but not in the "add" area. shut it off to go inside to get a quart of fluid, After we shut it off for a few moments it seemed to drive fine after that, shifted perfectly fine.

Just yesterday we drove it for a while, shifted perfectly fine... parked, ate lunch, got back in it, drove it to a fishing access, it sat for about 30mins and then once we went to leave, it was shifting hard again... drove it 35+ miles to get home, stopped at a gas station, turned it off for about 5 mins and went to leave it was shifting just fine

Is this signs of transmission failure or something relatively easy to fix? I want to change the fluid and filter, but with that high of miles on it I am afraid that it will do more damage than fix.

 

[melsg5]

as long as only change the filter and fluid, no harm, do not FLUSH the transmission. it sounds like you may have a sticky shift solenoid.

 

[Slicer89]

I wasn't going to flush it, just change the fluid and filter.

It shifts fine, but shifts hard randomly - and if the van gets shut off and sits for a little then it drives fine.

Someone suggested seafoam transtune and then changing the fluid as it may be the pressure control solenoid

 

[melsg5]

sounds like something to try

______________________________

 

[Slicer89]

I was just wondering mostly if anyone else could chime in before I do something that doesn't need to be done.

 

[erndog72]

My 2004 has been doing that for years. I tried changing fluid/filter, the seafoam trick, and even put in a shift kit at someone's recommendation. So far nothing has worked. There is a 99.9% chance it is the shift pressure solenoid needing replacement, but I dread doing that job. The job is fairly easy (see youtube videos), but accessing the component is a nightmare. Like you said the problem seems to come and go. Mine is mostly "come".

Item of note: If the shift from 1-2, 2-3, or 3-4 takes longer than 0.65 seconds twice in one trip you will get the P1811 DTC. Even though this will not illuminate the Malfunction Indicator Lamp (Check or Service Engine light), it does do a couple of important things. Via the PCM (Powertrain Control Module, also known as an ECM [Engine Control Module] in manual transmission vehicles) signals are sent to:

1. Freeze transmission adaptive functions
2. Record the conditions at time of DTC
3. Store P1811 in PCM history
4. MOST IMPORTANTLY - Command MAXIMUM line pressure

In other words, after P1811 is received, the transmission will shift hard by design, whether it was before or not. If the code is cleared out the transmission will shift smoothly again until it comes in again. Clearing the code is done by either a scan tool, or 40 warm-up cycles without a non-emission-related DTC occurring. The PCM will also cancel the default actions, evidently, when the ignition switch is OFF long enough to power down the PCM.

This may be more than you want to know, but I hope it helps you understand what may be happening.

 

[Slicer89]

My 2004 has been doing that for years. I tried changing fluid/filter, the seafoam trick, and even put in a shift kit at someone's recommendation. So far nothing has worked. There is a 99.9% chance it is the shift pressure solenoid needing replacement, but I dread doing that job. The job is fairly easy (see youtube videos), but accessing the component is a nightmare. Like you said the problem seems to come and go. Mine is mostly "come".

Item of note: If the shift from 1-2, 2-3, or 3-4 takes longer than 0.65 seconds twice in one trip you will get the P1811 DTC. Even though this will not illuminate the Malfunction Indicator Lamp (Check or Service Engine light), it does do a couple of important things. Via the PCM (Powertrain Control Module, also known as an ECM [Engine Control Module] in manual transmission vehicles) signals are sent to:

1. Freeze transmission adaptive functions
2. Record the conditions at time of DTC
3. Store P1811 in PCM history
4. MOST IMPORTANTLY - Command MAXIMUM line pressure

In other words, after P1811 is received, the transmission will shift hard by design, whether it was before or not. If the code is cleared out the transmission will shift smoothly again until it comes in again. Clearing the code is done by either a scan tool, or 40 warm-up cycles without a non-emission-related DTC occurring. The PCM will also cancel the default actions, evidently, when the ignition switch is OFF long enough to power down the PCM.

This may be more than you want to know, but I hope it helps you understand what may be happening.

The issue is so intermittent it's hard to tell what it is. Once it shifts hard, I can turn the van off for more than a minute or so and then it will shift smoothly again for a while, Sometimes it won't do it at all, or it can be like yesterday where even power cycling the van didn't help.