: STS 95: Hard gear shift



Alain3
09-05-04, 03:45 PM
My 95 STS shifts very hard. I can see a p076 error code current (transmission solenoid pressuse). I suspect I need to change the solenoid.
I had taken it to the Cadillac dealer but I took it back from them when they said I probably needed a new transmission and that it was going to cost me about $4500 to replace.
If someone confirms to me that indeed I need to chage the transmission solenoid, I'll take it to a transmission specialist and will diret them to change it hopefully without forking out the kind of money the deaker talked about.

Can someone tell me I'm doing the right thing?
Thanks for your help

elwesso
09-05-04, 04:19 PM
The solenoids are most likely the cause... They fail and cause crazy things... AS long as its not slipping, then you dont need a new tranny...

Search forums for SHIFT SOLENOIDS..... IIRC the kit is about $100, and its not really hard to replace.....

Welcome to the forum! thakns for signing up :wave:

Ranger
09-05-04, 10:45 PM
I have seen this scenerio over and over again. I can't help but wonder how many good trannies are trashed and how many countless dollars are wasted because of these incompetent or unscrupulous dealers and transmission shops.

Alain3
09-08-04, 06:15 AM
Thanks for the replies, confirming it's the shift solenoid. Now, I took it to an AAMCO transmission repair shop, told them to replace the solenoids. The guy siad I was absolutely wrong because bad transmission solenoids would not cause a hard shift, they would simply prevent the car from shifting. He said he needed to run a diagnostic for about $50 and he would tell me what was wrong. When I asked what it could be, he said it could be a number of things, including the auto speed sensor. Should I trust him and let him run his diagnostic?

foo
09-08-04, 01:41 PM
I can't voice any good opinion on aamco transmission shops.. my friend had some bad experiences with them... what I can explain to you is how the automatic transmission works... here's a short explanation of (at least the part that 'shifts')

shifting is hydraulically controlled....... there are 'clutches' and 'bands' in the transmission that 'snap' into place at t he activation of a solenoid which lets in the fluid (trans fluid) thus the hydraulic action.. If the fluid is under really high pressure it will happen much faster and cause a very firm shift which you can feel. This explains your code, there is more pressure in the system than it wants. This could be due to something as simple as needing to change the fluid or something complicated like the pump and pressure regulators and check valves, etc. Other simple things to check would be the temperature sensor(which adjusts the pressure based on the temperature of the fluid because cold fluid flows more slowly than hot fluid and if it thinks the fluid is cold and it's not then it will add more pressure).

A bad solenoid usually can not cause a very hard shift because all the solenoid does is open and close a valve to let the hydraulic pressure in........ worst case the solenoid won't open or won't open far enough cause either the transmission to not shift at all or to slip or even miss a shift causing problems.
Older transmissions worked solely off the pressure but the new ones are computer controlled so pressure does not matter any more in determining shift points.

I'm not 100% sure how this particular transmission works in the cadillac because I haven't taken it apart yet :> If it's controlled completely by computer then it should throw up some codes, which you saw.. If not then it has to be controlled by something such as a vacuum source, or the throttle cable. I'm guessing maybe the TPS on the cadillac helps control the shift points (by computer of course). But if the pressure is too high even when the computer is trying to lower it, it will shift hard.

Can you describe exactly what happens when it shifts? I can give you a better idea of what might be wrong....... Does it shift hard only when hot? or only when cold? Only when you hit the gas hard or only when you take off slow? Does it do it in all gears or just from 1st to 2nd, or from park to 1st or reverse, etc.. How hard is it really shifting? does the car lurch forward?

My first suggestion is to change the fluid and filter. You can do this yourself or have it done somewhere and make sure you use the right fluid. Lot of transmissions are real picky about the fluid :/ I don't think GM trannys are as picky as ford/chrysler, etc. Anyway, you can drop the pan and change the fluid (really only about half of it). or you can go to one of those places that has the fluid exchanger thing (not a pressurized flushing thing) and have them do it. Make sure they have one of those units that simply hooks up to the cooler tubes and lets the transmission pump the fluid through (the unit doesn't do anything itself it's just a glass tube with hookups at both ends and while trans pumps out old fluid it's sucking in new fluid without any help from the unit).. some people advise against this but i've never had a problem with it.

wow that was long winded :/ hope i didn't bore everyone to death hehe

eldorado1
09-08-04, 02:54 PM
LISTEN TO YOUR CAR!!!!!! It has more knowledge of it's internal dynamics than you do... Your pressure control circuit is somehow failing. It it sending the tranny full pressure, which is causing your harsh shift. But look on the bright side - it doesn't really hurt anything, in fact, it'll prolong your clutch pack life. Now, it is entirely possible your internal connection to the pressure solenoid may have failed, or the wiring to the trans connector, or the PCM (but that's a rarety) :suspense:

ljklaiber
09-08-04, 04:38 PM
Not really able to translate what you mean, but as for my own 95, the 1 and two trans positions are for towing, and sure grab when racing.

Perhaps you have some grab in all positions, ...just run it hard. bet it shifts just fine.

Alain3
09-08-04, 09:24 PM
First, thanks a lot to you guys out there. You are really helpful. Thanks in particular to FOO who gives a very clear explanation of things that are a bit complicated for a layman.
To answer FOO's questions: I have not noticed any difference whether it's cold or hot. It does it on all gears, including reverse, but it's more pronounced from 1st to 2nd, probably because the acceleration is greater.
Also two more bits of info: first that P076 code (transmission pressure solenoid) triggers the indicator "service engine soon" as soon as I start the car, which seems to indicate that the wrong pressure condition is present as soon as the car starts. Also, I have now noticed a new error code (history, though) which is P036, meaning "EGR valve pintle position out of range". Could that be related?

Thanks again for your nice help

foo
09-09-04, 12:10 PM
Hmmmmm.. LIke I said , I'm not positively sure what controls the line pressure in the tranny on the northstar.. I'll take a look in my service manual. On my 99 it says......(it's a different code on mine)...

The pressure control (PC) solenoid valve regulates actuator teed fluid passing through the solenoid into torque signal pressure. The PCM uses a pulse width modulated signal in order to control the torque signal pressure. The PCM compares various inputs in order to determine the appropriate pressure for a given load. The PCM varies the current to the PC solenoid valve from 0.1 amps, for maximum line pressure to 1.1 amps, for minim urn line pressure. An internal current monitor within the PCM provides feedback in order to determine actual PC solenoid valve current draw.

Basically means the computer changes amperage draw to the solenoid to increase or decrease pressure based on load (which i don't know how it determines but it probably doesn't matter at this point).......... when that happens it says:

# SERVICE VEHICLE SOON, SERVICE TRANSMISSION displays on the driver information center (DIC).
# The PCM commands maximum line pressure.
# The PCM freezes steady state adapts.
# The PCM freezes upshift adapts.
# The PCM freezes garage shift adapts.
# The PCM stores DTC P0748 in PCM history.

Which if it commands maximum line pressure it will shift hard, even chirp the tires between 1st and 2nd if you are hitting the gas hard.

You can try going into diagnostic mode and clearing the code and seeing if it comes right back.

If you haven't changed your fluid, i'd do that.. also it's probaly as simple as changing this pressure solenoid out or the wiring.. I'd start there.. fluid, and check wiring and possibly change that solenoid out. Before changing it out i'd clear the codes to see if it 'goes away' it could have been a one time thing and when you clear it, it will return the trans to normal.. I don't think you have anything to worry about.. As for the EGR, just take that out and clean it and put it back in :>

some things my manual says:

* Inspect the wiring at the PCM, the transmission 20-way connector, and the PC solenoid valve connector for the following conditions:
* A backed out terminal
* A damaged terminal
* Reduced terminal tension
* A chafed wire
* A broken wire inside the insulation
* Moisture intrusion
* When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

AdibT
10-01-04, 07:26 AM
My 95 STS shifts very hard. I can see a p076 error code current (transmission solenoid pressuse). I suspect I need to change the solenoid.
I had taken it to the Cadillac dealer but I took it back from them when they said I probably needed a new transmission and that it was going to cost me about $4500 to replace.
If someone confirms to me that indeed I need to chage the transmission solenoid, I'll take it to a transmission specialist and will diret them to change it hopefully without forking out the kind of money the deaker talked about.

Can someone tell me I'm doing the right thing?
Thanks for your help

[Quote]
Dear Alan,
I had the same problem with my Councours 1994 and, after changing the selonoid, the PCM and checking all wires, I still have it!
Please can you inform me how you solved your problem?
Thank you.
Adib

parts68
03-31-06, 08:46 PM
this may be an old post,I dug it up after having same problem on a 95 rora.
I had an identical car to experiment with and switched the PCMs and problem followed the PCM.
First car now shifts normally and second car has the code P076 and shifts hard.
I probed the PCM wiring connector for PCS(pressure control solenoid) and it read 4.6 ohms just as it should.
This means its in the PCM,just trying to figure out if its the chip or main PCM.
Also I know I read somewhere but cant find it that someone else had a similar problem and had the PCM reflashed and it cured it.
Dealer said that the 95s cant be reflashed and top tech said he didnt think that the chip was bad but more so the PCM itself.

eldorado1
03-31-06, 09:08 PM
the PWM circuitry is suspect. A chip won't fix it.

It's worth a check to see if any of the the pins are corroded though.

parts68
04-01-06, 10:08 PM
switched PCMs and problem followed it.
no corrision at the PCM terminals.
I get the correct values for PCS at the PCM
and both cars work fine when I use a good PCM.

acklac7
04-02-06, 01:57 AM
Just wanted to chime in with my PO76 problem...Since it appears to be a rare occurance....I got my Trans. rebulit about 2 years ago and ever since P076 has been popping up VERY infrequently (about once ever 2 months) ever since. 95% of the time the code will get thrown right after I start my car...I believe it has only been thrown once while driving....And that was the first time it set....The symptoms are the similar..Slamming into reverse...Rough shifting etc...However I have found that 95% of the time the code will go to history if I cycle the ignition (turn the car off then on)...Which makes me wonder whether the PCM is acting up???...At any rate it hasn't become a major problem..yet..Hopefully it never will (croses fingers)

parts68
04-02-06, 09:02 AM
it will rip your engine and tranny mounts
ask me how I know
If the PCM replacement cures mine it will most likely
cure yours also

clarkz71
01-06-07, 06:19 AM
What's with your post's my1stcaddy? Are you asking a question?

eldorado1
01-06-07, 11:18 AM
drunk poster or spammer. Pay no attention. Move along, nothing to see here.

acklac7
01-07-07, 01:24 AM
drunk poster or spammer. Pay no attention. Move along, nothing to see here.


LOL...Guess it got deleted already...

Thought I recognized the thread....Just wanted to add I haven't gotten a P076 since my post on 04/02/06...Trans. runs like a champ ;)

Sidney Ash
08-29-14, 11:51 PM
parts68, can you tell me which pins you probed for the PCS?

E-mail deleted

thank you

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Ranger
08-30-14, 10:28 AM
Look at the thread dates.
Parts68 hasn't signed in since 04-04-14.