No downshift

[Richard STL]

Vehicle 1992 Buick Century
Engine Type: 3.3L V6 MPI OHV 12V Engine Code N
150K miles
Automatic Transmission
Clean and full of ATF (maybe a little overfull)

After sitting unused for about 10 days in cold weather, I drove it to about 10 miles, it sat for about 30 minutes and I drove back home. On the way home I slowed down to a stop and it acted like a manual transmission in a high gear, it bucked and killed the engine. I restarted it in neutral and revved it a little and put it in drive and it seemed fine until I stopped again.
Then the same thing happened.

I've done a little online research and it appears to be a bad TCC lock-up solenoid. After driving it again the problem did NOT re-occur.
Is it reasonable that the problem was weather or temperature related?

[jgate]

Weather related ,For now perhaps, really hard to tell you did drive the vehicle 10 miles before stopping, this would give the trans plenty of time to warm the fluid. More likely that the sitting for a long period of time in the cold weather had more to do with the unlocking problem. But still shouldn't of caused a problem,.The TCC solenoid does have a rubber "o" ring that might of become swollen and momentarily stuck on in the bore.
There is also the 2nd clutch pressure switch , wired in series with the TCC solenoid electrical ground circuit, this switch provides a ground for the TCC solenoid at a calibrated pressure,This allows the TCC to apply only above a certain vehicle speed.
Then you also have the 3rd gear pressure switch, Wired in series with the TCC electrical circuit, this switch is normally open. The 3rd clutch pressure switch is closed in third gear by 3rd clutch fluid to complete the TCC circuit. This allows the TCC to apply in third gear only.
In third gear with the appropriate driving conditions, as determined by the ECM, solenoid signal fluid pressure shifts the converter clutch control valve against line pressure. This redirects the orifice line pressure into the converter apply fluid circuit to apply the TCC. The torque converter clutch solenoid is an electrically controlled exhaust valve, and when energized by the ECM , it shuts off exhausting solenoid signal fluid at the converter clutch control valve. The closing of the solenoid valve causes the solenoid signal fluid pressure to increase and shift the converter clutch control valve, This applies the torque converter clutch.
It is always advisable to replace the TCC solenoid along with the 3rd gear pressure switch.
These are located under the auxiliary side pan, located on the auxiliary valve body.

[Richard STL]

Thanks for the detailed explanation. Unfortunately I'll need to read it a few more times to understand it.

I drove it again last night in moderately cold weather and it did the same thing. After Revving and shifting into drive I got it going again. And on the way home it seemed like it reset and did fine.

I think I know why I did NOT have a problem the second time I drove it because I never got up to highway speeds. I probably didn't get over about 35 mph. Also it was a relatively short there and back drive.

I heard you can unplug the the Tcc lock-up solenoid and prevent the lock-up problem. Is there any other downside to doing that other than decreased gas mileage?

[jgate]

Yes you can unplug the the TCC,If this is the TH125 trans, the 92 century came with 3 different trans, the th125, the 440t4 trans and late in 92 the 4L60e. If it would be the 440T4 trans you would just have to cut the appropriate wire, for the TCC lock up circuit.
So if this is the TH125 trans, the only difference would be a slight increase in fuel consumption and of course no converter lock-up.other than that should not cause any problems. I used to see these all the time, i would say about 30% of the TH125 lock up trans coming in with the TCC unplugged.

[Richard STL]

OK. I unplugged the TCC and the lock-up problem seems to have disappeared. However the Service Engine Soon light comes on and goes off after a few seconds. I checked the error codes and it blinked a 26, 27 and 28
26 - Quad Driver Module (QDM A) error
27 - throttle switch open
28 - Auto Transmission Range Pressure switch error
I assume these are related to unplugging the TCC?

I looked up the step-by-step procedure for replacing the solenoid and it was very involved.
However it looks like there is enough room to simply unbolt the cover and get easy access.
Am I missing something here?

[jgate]

First thing , do you know what model trans is in this vehicle?
You will find the codes on the spare tire cover, there will be a white sticker with all your
vehicles codes, you would be be looking for code ME9, M13, OR CODE MD9.
Have you looked to see were your trans mount is? Some are on a bracket
mount, this type will be more involved as it requires the removal of the trans/engine
mount. That requires removal or the bracket mount and using a transverse engine
holding tool , to hold the motor because it is a trans/engine mount.
Some have the mount just before the pan that doesn't have to be removed to
remove the pan.
The pan is only about 1/2 inch deeper than the valve body that is under this pan,
so you will need clearance the depth of the pan plus the width of the valve body
( approximately 4") to remove this pan.
As far as the codes that are popping up,is because of unplugging the trans terminal.

The "Quad Driver" is a device in the computer that "drives" electro-
mechanical devices in the car. Computers run with very little current
milliamp or micro amps in their circuits. But the devices that
turns on your cooling fan, bulbs, or emissions relays may require
current in a higher range, say tenths of an amp.

Thus, the computer can't talk very well with such a high current
device. It needs help, and it gets in in the form of this Quad Driver
device. The computer sends a signal (very low amps) to the driver, and
it in turn then signals the electromechanical device to do whatever it
needs to do with a higher current which that device can use.

One more thing do you have this type of bracket around the pan? (check the attachment)
Let us know the code to the trans, so we know what trans we are dealing with.

[Richard STL]

The transmission does NOT look like the diagram in the attachment.
The Code on the spare tire cover is MD9. It looks like the cover is pretty easy to get to and remove.

As for the error codes and the Quad Driver...
Will driving the car with the TCC unplugged cause any damage? Electronic or otherwise?
With the snow and ice we're expecting here in St. Louis, it doesn't look like I'll be getting to work on it anytime soon.

Thanks jgate for all your help on this.

[jgate]

OK the MD9 code is for the TH125/3T40 trans.
This should be an easy one to change the solenoid
and pressure switch. The trans mount should be just
before the pan. Like I said just make sure you know were
trans the mount is , and don't remove it unless you have
the transverse holding tool.
As far as the electronics go , you have 4 QUAD drivers
in this PCM, this one is for the trans, should not effect
any other circuit. should not be a problem.

[Richard STL]

I just realized I forgot to post that "All is Fixed"
I replaced the TCC Solenoid without a problem, and topped off the fluid and all is well.

Thanks again;
Richard