TCC stopped working

[LMP]

'93 TS, 3800
Was at steady highway speed, about 105 km/h, in 4th + TCC applied...and progressively, within about 2 or 3 seconds, TCC released. COntinued in 4th, cruise control still operative, no code. I continued the run to destination, about 5 miles ahead. ON the return leg, TCC never applied. All 4 gears + cruise control continued normal operation.

Most causes in the book relate to internal failure....O-rings, seals...and the like.....or, command failure from the PCM. THis last one is simple to verify, as it is possible to bypass the PCM and provide a solid ground to either or both TCC solenoids (apply and PWM).
www.avigex.ca/xport/transaxle.jpg

NOt a priority at this time as winter is a deterrent to such initiatives and I use the car just occasionally....but I will report findings when time comes.

[Tech II]

Could even be a bad brake switch, too....really need a scan tool to diagnose this, by seeing all the inputs to the tranny....

[LMP]

Originally Posted by Tech II

Could even be a bad brake switch, too....

Negative. Brake switch would inhibit cruise control. That is why I specified.

[500hpgtx]

After trouble I had with my 4T65-E trans on my grand prix, I would think it more than likely that the TCC internal switches are faulty. Guess you would have to remove the side cover to get to them. I am sure you are thinking the same LMP....best of luck

[Tech II]

Was throwing that out there as a possibility.....the TCC circuit in the brake switch, I believe, is separate for the cruise....was thinking it should be checked out BEFORE DIVING INTO THE TRANNY....

[LMP]

http://www.avigex.ca/xport/transaxle.jpg
single contact for TCC+cruise.
....will not dig into that before this coming summer. Running in and around town rarely goes above 50 mph so TCC is not enabled anyway.
I have another condition with a code (will read within a few hours) that keeps radiator fans running right at KEY ON (eh..this is winter here...)..I had that a few years ago but I can't remember what it was....probably a false HIGH TEMP reading...

[LMP]

Originally Posted by LMP

... I have another condition with a code (will read within a few hours) that keeps radiator fans running right at KEY ON (......

...funny...GM apparently was not aware of the great white north..
.DTC 15..that is low temperature reading..YES..it is cold here!
DTC15 as well as DTC 16 (HIGH TEMP) both turn the fans ON ....
yes temps here at this time go to or very near the alarm limit...-36°F in description of code (or even -22F according to their trouble shooting )and indeed yesterday, I took the car from inside the garage...no DTC....but then the car spent the day parked outside and when I started it then DTC15 was set. OUtside temp yesterday was quite low and after 22 years, the thermistor can also be forgiven to have shifted a little, reading a bit lower than real....

It will go away when in the garage or when outside temp go up.

EDIT: Went out this morning...CEL gone now....

[LMP]

New developpment: I have 3 codes now: DTC15 Low coolant temp, DTC44 O2 sensor lean, DTC56 QUad B driver (drives the 3 EGR ports...that I know for intermittent failure on one port)..but also drives TCC duty cycle PWM solenoid....

But.... CEL comes ON and TCC comes back ON when I tweak OFF the engine temperature thermistor.... . ALso some engine misses and hesitations .
....when I tweak in the temp sensor , CEL goes OFF but TCC goes OFF too.

Obviously I have an electric problem......may be corrosion in connector C111...I have some historical reasons to investigate there.....
...will come back when new facts arise ...

[500hpgtx]

May be helpful to clean the grounds and tighten the connectors. I have avoided a lot of headaches by making certain that I had a very solid ground before getting into electrical issues...good luck

[LMP]

SOlved.
20 years ago I had spliced the wire from the engine temperature sensor to computer...adding a switched parallel resistance to tweak the reading in cold weather. ( explanation: By very cold temperatures the engine control stays in open loop too long and burns excessive fuel. WIth the tweak, that I switch in after a few minutes of operation, the computer is forced with a false higher temperature reading that makes it turn faster into the closed loop mode, with a significant increase in cold weather fuel mileage. )
But 21 years later, that is now, one wire quit.(temp sensor side)

.and the computer was left without a reading unless I switched in the 80°F tweak (2200 ohm resistor)
a) --without the tweak the computer popped a code (LOW TEMP), but let the 4 speed + TCC working.
b) --however switching the tweak in was equivalent to a temperature of about 80°F: code would go extinct but 80°F is not high enough to enable TCC...(computer happy to have a reading but it waits for 140°F)

Everything is soldered back as it was supposed to be...and all is OK now.

[tinkering]

Could this somehow relate to my problem?

I am having an idle speed problem. It is idling high, causing it to clunk hard into reverse and forward. It is shifting hard too in certain conditions.
This seems to have come around after I replaced the temperature sending unit for the dash gauge. The dash gauge needle never comes right up to ride in the middle or normal running position. I noticed the sending unit connector has two or three wires on it. Could it be that the computer is keeping a high idle while waiting for the operating temperature signal (which never comes)??

I changed out the thermostat, hoping that would bring the gauge up but to no avail.

[LMP]

A very low temp reading can keep a high idle....but this should pop a low temp code...

The dash temp sensor and the computer temp sensor are not the same (but you seem to be aware of that). . ....one is located near the thermostat, the other...never saw! Computer sensor has 2 wires, the other only one (according to diagram) ..though this is not clear as RockAuto tells the 2 pin can be used in place of the one pin...

www.avigex.ca/xport/enginesensors1.jpg
www.avigex.ca/xport/instrumentpanel1.jpg

The dash gauge sensor has no connection to the computer hence cannot have an effect on idle.
My temp indicator has always run low...indeed...
I'd rather suspect the idle air valve...or the throttle position sensor. A faulty TPS eventually will pop a DTC 21 or 22 code...but not always..faulty TPS (with a code) will inhibit 4th gear and TCC and cruise control.
Are you able to read the codes from the dash CheckEngineLight?

A loss of vacuum to the transmission pressure modulator (or failed modulator)
http://www.avigex.ca/xport/modulator.jpg (arrow)
will also keep a high oil pressure causing hard shifts.

[tinkering]

Originally Posted by LMP

A very low temp reading can keep a high idle....but this should pop a low temp code...

The dash temp sensor and the computer temp sensor are not the same (but you seem to be aware of that). . ....one is located near the thermostat, the other...never saw! Computer sensor has 2 wires, the other only one (according to diagram) ..though this is not clear as RockAuto tells the 2 pin can be used in place of the one pin...

www.avigex.ca/xport/enginesensors1.jpg
www.avigex.ca/xport/instrumentpanel1.jpg

The dash gauge sensor has no connection to the computer hence cannot have an effect on idle.
My temp indicator has always run low...indeed...
I'd rather suspect the idle air valve...or the throttle position sensor. A faulty TPS eventually will pop a DTC 21 or 22 code...but not always..faulty TPS (with a code) will inhibit 4th gear and TCC and cruise control.
Are you able to read the codes from the dash CheckEngineLight?

A loss of vacuum to the transmission pressure modulator (or failed modulator)
http://www.avigex.ca/xport/modulator.jpg (arrow)
will also keep a high oil pressure causing hard shifts.

I am not with the vehicle right now so I will try to get someone to read the codes from the dash.
I was wondering about the TPS. I will look into the IAV too.
I have a new vacuum modulator that I have meant to install for a few years or more.

Thanks LMP.
I will get back with results as they develop.