Buick Century TCC Fault Code

[Jetmechof7s]

Hi,

I have a 1994 Buick Century with a TCC issue. The car has only about 74,000 miles on it, and is in great shape.

After about 40 minutes of driving, the car drops out of Overdrive, and the TCC drops out too. This occurs on level roadway, with no additional throttle demand.

Once this happens, it'll never go into Overdrive again, until I shut the engine down, and restart (I can do that while it's rolling, or stop first). After that, the P0740 (TCC Circuit Malfunction) code will be gone from the current faults, and the car will go back into Overdrive (The fault code will remain in the history). Usually within a minute or two, it'll fault again, and drop back into Third Gear. Once it has totally cooled (such as while I'm at work, or over-night), I'm good for about 40 minutes, before it happens again.

The car had been sitting alot and the hydraulic fluid was a little dirty, so I had it flushed, hoping it would go away. No such luck.

Does anyone have any ideas?

-Maybe just a weak solenoid valve that gets hot and won't hold anymore? It never fails to engage initially, when I first get to the highway. It really does take about 40 minutes, to happen. I find it odd, that once it does, it won't go into Overdrive again, even for hours! -but it will after it totally cools down.

If that's it, how hard is this to change, and how expensive? Do I have to remove the torque converter, trans, or anything else?

Thanks!

Patrick

[oldscsc]

How did you get your codes? If you have a scan tool hook it up and see if the TCC is being command on by computer. If it is being command on and is not engaging then I would look at he TCC solenoid and wiring.

Solid advice. I'm afraid, however, that once the computer stores a current fault for the TCC failure it will no longer command it on. Guess we'll wait and see.

[Jetmechof7s]

How do you get a P code out of a '94 model year???

I got it from the computer, and the scanner.

[Jetmechof7s]

Solid advice. I'm afraid, however, that once the computer stores a current fault for the TCC failure it will no longer command it on. Guess we'll wait and see.

If you read my post, you'll notice that I can make the current fault go away, by turning the car off, then back on. The fault remains in the history, but the current one goes away, at least until it's been in Overdrive again for a few minutes. It never has a problem going into Overdrive, until the fault code sets. Again, this takes about 40 minutes of driving, as long as it was cold, when the drive began. Once it sets however, it won't go away without turning the engine off. When I turn it back on, the car goes into OD again, but usually only for a few minutes, max. -once for maybe 14-15 minutes. Also, parking the car for several hours will make the current fault go away, and make the car work fine for that 40 minutes or so.

[oldscsc]

If you read my post, you'll notice that I can make the current fault go away, by turning the car off, then back on. The fault remains in the history, but the current one goes away, at least until it's been in Overdrive again for a few minutes. It never has a problem going into Overdrive, until the fault code sets. Again, this takes about 40 minutes of driving, as long as it was cold, when the drive began. Once it sets however, it won't go away without turning the engine off. When I turn it back on, the car goes into OD again, but usually only for a few minutes, max. -once for maybe 14-15 minutes. Also, parking the car for several hours will make the current fault go away, and make the car work fine for that 40 minutes or so.

I read your post. Did you read mine? Post #6. I gave you all the info I knew off the top of my head. I'm out of ideas...that you can do with basic hand tools, that is.

[Jsdirt]

I got it from the computer, and the scanner.

I learn something new every day!

[Artey72]

I learn something new every day!

Some 94 model GMs had the earliest obd2 systems on them.

[Jetmechof7s]

I read your post. Did you read mine? Post #6. I gave you all the info I knew off the top of my head. I'm out of ideas...that you can do with basic hand tools, that is.

I did some calling around to auto parts stores, and discovered that they don't all seem to be sure of what I'm asking for, when I ask for a TCC Solenoid Valve.

Some think I'm asking for a "shifting valve", of some sort. I'm thinking that isn't it!

I'm wondering if there's another name for this part....

[Jsdirt]

I've given up on Advance Auto, C.A.P., or Auto Zone (depending on where your located). 98% of the people that work there haven't got a clue. I've had good luck with NAPA - not just in customer service, but quality of the parts as well.

 

 

Some 94 model GMs had the earliest obd2 systems on them.

Ahh .. I always thought '95 was the cutoff year. I should know better than to assume ANYTHING that is automotive-related by now ...

[Jsdirt]

How do you get a P code out of a '94 model year???

[Carder09]

Being you swapped the old fluid, one problem is very dirty fluid full of metal particulates that can obstruct the function of the tcc, so that can be either the tcc solenoid itself, or the wiring harness and connector, and maybe the pcm itself. There is a long t/s check that you can do but you will need to make or find some 20 pin jumper wires to do certain parts of the check to include a few other things.

[txab]

You might ask your question on one of the Buick forums to see if anyone has had the problem.

 

https://www.google.com/search?q=buick+century+forum&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb

 

 

Also let a transmission shop at least take a look at it and give you an estimate

[Jetmechof7s]

I've given up on Advance Auto, C.A.P., or Auto Zone (depending on where your located). 98% of the people that work there haven't got a clue. I've had good luck with NAPA - not just in customer service, but quality of the parts as well.

 

 

 

Ahh .. I always thought '95 was the cutoff year. I should know better than to assume ANYTHING that is automotive-related by now ...

Now that you mention it....I thought it was 95 as well. I didn't even think about it when I scanned the car's computer.

-And you're right, about auto parts stores, these days. It used to be, that retired or otherwise injured mechanics worked there. Now, it's people with absolutely no clue!

[Jetmechof7s]

How did you get your codes? If you have a scan tool hook it up and see if the TCC is being command on by computer. If it is being command on and is not engaging then I would look at he TCC solenoid and wiring.

I did hook-up the scanner, and like I said, it does go into Overdrive and lock-up....but then it faults, showing the above code, immediately un-locking TCC clutch & dropping out of 4th & into 3rd. The fault stays until I shut the car off. When I re-start, it's gone, but still in the history. If the engine / trans are hot, it'll drop back out of TCC lock and 4th within a few minutes. If it's cold when I start it again, it'll be good for about 40 minutes. Today was unusual...it didn't fault for nearly an hour. Normally, it'll fault and drop out in almost the exact same location!

-Make that yesterday.....Monday.

[Duelin]

How did you get your codes? If you have a scan tool hook it up and see if the TCC is being command on by computer. If it is being command on and is not engaging then I would look at he TCC solenoid and wiring.

[oldscsc]

Components of the TCC system:

 

-Solenoid (and accompanyng fluid flow when activated)

-Torque converter clutch itself

-Wiring and connector from PCM to valve body

 

When the PCM sees fit, it will activate the TCC solenoid by providing it a path to ground. The solenoid moves positions and now allows pressurized fluid to reach and apply the torque converter clutch, which reduces heat output within and transmission, increases efficiency, and lowers engine speed by 200-300 RPM.

 

Since you said the car drops out of overdrive when the code is present but will enter overdrive when the code is not present, the two are probably related. The lack of overdrive puts you in 3rd gear, (usually 1:1 on a trans that old) which is usually the failsafe or limp mode gear.

 

Without advanced diagnostics (hydraulic pressure testing or computer diagnostics due to lack of OBD II), you are kind of stuck. Trans shops have a bad habit of not diagnosing anything and telling the customer they need a complete rebuild. At under 80,000 miles, you probably don't.

 

I don't normally condone throwing parts at a vehicle and praying, but considering the price of a trans shop's diagnosis alone versus the price of a new TCC solenoid, you could throw a TCC solenoid in the car and see how it performs. It may or may not fix the issue, but for ~$50, its worth a shot.

 

Keep in mind the code for a TCC solenoid says "circuit malfunction" for a reason. There's an issue, not necessarily with the solenoid itself, but with the entire control circuit, including the solenoid. Be sure to check any wiring you can get to for breaks or tears on the insulation before and during the repair, if you choose to do so.