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2001 Pontiac Montana Shifts Hard Sometimes

The transmission on my 01 Pontiac Montana shifts hard sometimes. When it does this I can turn it off and let it rest for about 30 seconds and then the hard shifting may go away. It has 60K miles on it and am planning to do my first transmission pan drop, gasket and filter change soon. I let the shop do this task a 30K. Is it worth it to also change the “vacuum modulator” while I’m at it? My Haynes manual suggests that this may be the fix. How hard will this be do do for a neophyte, shade tree mechanic?

You need to scan the computer for codes. When the transmission starts to shift hard, take it directly to one of your local auto parts stores who will usually scan the computer for free. DO NOT shut off the ignition once it starts shifting hard, just get a scanner hooked up to it and post back here any code/s which might come up. As far as a vacuum modulator is concerned, don’t bother. This transmission (4T65E) doesn’t have one.


thanks for the reply transman…

When it starts to shift hard the check engine light does not illuminate. The local parts stores (i live in Oakland, CA) will not scan codes for free. they demand that you buy the scan tool; they will not rent it out either. if the check engine light is not illuminated or flashing is there any code to be read?

Because it is due for the transmission pan drop and filter change out, is it still advisable for me to attempt this task in my backyard. I have never done one before, but i think i am handy enough based on the directions in the Haynes manual and my lack of extra money at this time.

Doing the pan and filter is no big deal. The only thing you don’t have is the experience to “read the pan” should there be unusual things. Other than that is is just exercising lots of care - you want a good torque wrench and follow the torque specs for the pan. You MUST use the right trans fluid (Dexron IV). You MUST leave the pan completely clean - not so much as a piece of lint from a rag. Stuff like that.

As for the shifting issue, without a code it is really guessing - but here is a really good guess for this transmission: its called the EPC (electronic pressure control) solenoid. Google it - you’ll get plenty of info. You can specify 4T65E as the trans type. If there isn’t a code now, it will eventually set one.

You can get a lot of good info on this trans here: - including the harsh shifting.

Thanks for the information cigroller…I checked out the link. According to Norris EPC is likely the issue AND it require a tear down. I’m not in need of that just yet, so I’ll wait till I get farther down the road. The description of when the problem occurs was spot-on… Still no check engine light yet.

I have a beam type torque wrench that reads foot-pounds. According to Haynes, the torque spec for the pan bolts is 120 inch-pounds [120*0.083=9.96 foot pounds ~ 10 foot pounds] and a claimed capacity of 7.4 quarts of Dexron III fluid.

Will be at it soon… Thanks!

I believe Dex IV supersedes Dex III.

The EPC solenoid can also be replaced without a teardown. It can be accessed through the side cover - its a little tricky as the subframe has to lowered to get at it. But is can be done with the trans intact and in the vehicle.

Even so, that’s probably something you’d want to pay someone else to do. As such, even though its a good guess you’d want to be sure before you spent the $$ to have that done - in case it is something else and worse.

If you can do it yourself it may be worthwhile as a “guess” - just b/c the part itself is not so expensive.

If transman returns to the thread, take any of his corrections over anything I’ve said. He’s got all of the experience. I’ve just got an Olds Sihouette.

I agree with you cigroller, transman is the expert on trannys.

But: He mentioned the 4T65-E.

pacecar, if you have the same Haynes maual (#38036) I have we’re looking at a different tranny.
This one is 4T60-E.

Differences between them,???.

Remember now, the first paragraph tells you how to test the modulator to see if there IS anything wrong with it.

I couldn’t give you any intelligent technical info on the differences between 4T60 and the 65. But I believe that the 60 was gone by about '98/99. By '03 they were all 65s.

I had a 2000 Silo, but I can’t for the life of me remember which one it had.

Anyway, it had the same quirks.

Yes, I have the same Haynes manual (#38036). Page 7-5 provides the check for the vacuum modulator, but the manual does not specify when the shift from 4T60-E to 4T65-E took place. I’ll trust transman on this one. I got further confirmation because I could not find a vacuum modulator at for my specific make/model/year (Pontiac/Montana/2001). I have been under the van doing oil changes several times and can’t remember the model number stamped on the tranny pan.

It is my wife’s van and I just dropped her off for school in it; it ran like a dream (highway and city streets) with flawless shifts.

OK, so I finally got a “Service Engine Soon” light. This happened a few days after changing the air filter, draining/refilling the coolant, an oil change, and transmission pan drop and new filter. All went well with the DIY service event in the backyard. Hard to believe given my luck.

To read the SES I bought a code reader. The codes were P0122 (Throttle position sensor circuit, low input) and a pending code P1635 (5-volt reference circuit). I put a multimeter on the connection to test the PCM and the wiring. They checked good. I did not back prob the TPS figuring for $30.00 (the price of the TPS) I could replace it myself. Well, the TPS is on the backside of the throttle body up against the firewall. I’m really wrestling to get the throttle body removed. My Haynes manual is less than helpful. Is there any chance that replacing the TPS will make the transmission behave better? Some folks on the internet think so.

$30 or not you can check the TPS - b/c the problem might not be the sensor but its wiring instead. Checking these is pretty easy (locating a wiring fault, if any, might not be).

I believe that the TPS input is almost always used in transmission control - but somebody smarter about it than me would have to comment. It surely can’t hurt.

TPS is definitely used in transmission control. The TPS takes the place of the TV cable from the older transmissions. The more you push down on the accelerator the more line pressure is increased through the EPC. So, yes the TPS can cause harsh shifting. I’ve posted this image before and here it is again, prime example. I took this snap shot with my scanner some time ago. Car came in complaint of dropping out of overdrive into 3rd at highway speeds. Another shop wanted to sell her a new transmission. What I found was TPS maxing out at 4.94v. You can see the spikes on the bottom half of the screen. Even sitting at idle in park it would spike which was telling the computer that the driver was flooring the accelerator. Well, owner on expressway 70mph, TPS maxes out, transmission kicks down to 3rd just like it should. That other shop saw her coming. I put a $50 TPS on it and sent her on her way. Told her ALWAYS get a second opinion.


transman, where is your shop? I don’t care how far it is, I’m just going to start shipping my transmission issues to you from now on. Does UPS take minivans?

Hi cigroller, the wiring and the PCM checked good. So the failure should be in what’s left, the TPS. The TPS was cheap – $30.00. Getting the throttle body off, is a pain in the back. I got almost everything disconnected, except (I think) two coolant lines connected to the throttle body. I thought they were gas lines and got nervous. In any case, Saturday (4/24) I attack again. I read further and know I must drain some coolant (again!!!) and then pull things apart including the coolant lines on the TB.

Hi Transman,

Good to know. Well, here’s to hoping that the replacement of the TPS gets the transmission to calm down. The van is in great shape otherwise.

I second cigroller. I’d like to ship my transmission issues to you from now own. I’ve a got a 1996 Buick LeSabre with transmission morning sickness…

Ha, LOL…I just do bench jobs at my shop. I farm out all the R&R work mostly to my brothers shop. This young lady, a friend of my brother is from out of state and couldn’t afford a $2k overhaul bill so he had her come see me to see if it could be anything else. Little quick stuff like that I’ll knock out here.

She was ready to cuss out the other shop. I gave her a print out of my scanner snap shot because the other shop charged her a diagnostic fee and she was going to go get that $$ back. I don’t blame her.

Hey, if the Fed-ex guy comes by my shop with a large crate and a mini van in it, I’ll think of you.


Just an update… My wife and I got the throttle body off. I replaced the throttle position sensor as indicated by the SES light and changed out the idle air control valve because I was there. The throttle body was pretty grimy. I cleaned it up pretty good with some TB cleaner and a brush. After getting everything buttoned back together I cranked it and took a drive. The SES light did not come back on AND the clunk in the transmission disappeared.

Thanks for the help CarTalk Community!

my 2002 montana does everything it should except it makes its first upshift at about 26 mph ( 40 kmh for us canadians ) and second shift at about 37 mph. no codes clean pan