Hey guys,
My Camaro has been having problems with its lockup converter in the 700-R4 automatic, which is linked to my LH0 3.1 L V6 Engine. It seems that the car will refuse to lockup its torque converter on random occasions. The car will lock it up on occasion, but if it does its usually during times less than 1/4 throttle, and it won't be long before the torque converter unlocks again (10 secs or so), no matter where the throttle is. My car is bone stock, it shifts fine and accurately in every gear at any point of throttle, but wheres my lock up gone boys? I was going somewhere and it worked fine, then all of a sudden I went home and it didn't want to work anymore. Something obviously stopped working (computer or sensor somewhere). Give me your thoughts as I like to be driving on the highway in the summer, not being limited to roads below 45 mph.

 

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could be a number of things but you need to do some testing first.

(1) make sure the wiring is OK to the tranny and not loose or anything.

(2) use a test light hooked up to the ALDL connector to monitor the TCC lockup signal. See if the computer is commanding the convertor to unlock when you notice it unlocking. you can search the archives or the tech articles here for info on how to do this.

(3) make sure your brake switch isn't messing up. when you tap the brakes there is a switch that removes the ground from the TCC solenoid which then immediately unlocks the TCC solenoid. You can check this by using a continuity tester or something.

 

Thanks, I am gonna rig up a test light to my connector to monitor unlocking/locking. If the trans is running good and shifts fine and does unlock, if only for a short while, that means its most likely a computer problem right?

 

a "computer" problem is very unlikely.

possible causes include:

bad sensor data for the computer to work with (a jumpy TPS maybe?)

loose/defective wiring to sensors or to transmission

defective TCC solenoid (have to drop the pan to fix this one)

bad switch on the brake pedal which disables the TCC

 

I see alot of bad TCC Solenoids. They crack where the ball seats and causes leaks. Thats not an intermittant problem though. When it cracks, you usually lose TCC all together.

Like the others mentioned, could be a bad brake switch, a faulty sensor (Coolant temp, TPS, etc...) If you had a scantool or Datamaster, you could compare sensor data -vs- TCC operation to help isolate it. FYI, the brake switch has several seperate circuits going through it. You can't rule out the switch because the brake lights work.

 

I did replace the computer w/ a crappy Borg Warner one, because my ignition control module kept dying, but the computer was NOT killing it, contrary to what somebody told me. Thats a different story, anyways, I think its the computer, but you guys say its the coolant temp sensor or TPS? I hear TPS has nothing to do with the lockup or control of a 700-R4. What would coolant temp sensor have to do with it? Do brake switches die randomly? You say if my TCC solenoid is shot, then I will have no lockup at all, I guess I will have to check my trans wiring and the connector with a light, just to see if its at least a computer problem. I appreciate all of your help with ruling this problem out, I will try to see whats going on so I can go other places than this town.

 

The TPS has a hand in the matter because at about 75% of throttle position, the ECM goes into Power Enrichment mode in which the ECM disables the TCC lockup function. Its unlikely, but possible that its spiking fast enough to unlock the TCC but not enough to change engine performance. Its unlikely, so I wouldn't consider it unless all else checks out OK.

The coolant temp sensor sends engine temp to the ECM. The ECM will not allow TCC lockup below a certain temp. If the sensor was bad, it may fool the ECM that the engine was cooler than it really was which would allow the engine to run but not allow TCC lockup.

As for the brake switch, I usually see them cause Cruise Control problems from burnt contacts, but its possible that the same scenario could apply to the TCC circuit of the switch.

 

We don't know. this is where you take over the job, and do some diagnostics to rule out the suggestions we've given. You don't want to just go replacing parts until the problem goes away (didnt get you far on the ECM did it?), it's better to do a little bit of diagnostic work to understand the problem and rule out things.

 

Ditto what he said^ We are giving you suggestions of what to check out and possibly rule out as the culprit. Nobody said anything about replacing them. If you find that something is indeed bad, then replace it. If you don't give a rats **** about diagnosing or understanding the problem, and have a fat bank account, then I'll go ahead and give you a list of everything to replace...

 

Okay,
I have gathered some more information on this problem. I hooked up a test light to my computer diagnostic connector (The shift light prong which tells when the computer is telling your Torque Converter to lock or not), and the computer is not telling the car to lock its torque converter at the appropriate times. The torque converter will lock up on occasion, and when it does the computer light that I have rigged up goes on, when I take my foot off the gas, or hit the brake pedal, it goes off for obvious reasons. But when I am doing 60 down a highway it will not light, and the car does not lock its torque converter. All of this information tells me that this problem is computer related. Many of you have said that the Coolant Temp Sensor may be to blame, and I have some more info on that. In the summer, my fan does not turn on when it is supposed to, it will only work unless the A/C is on, or sometimes the fan just feels like working and will turn on. That could mean my CTS is bad, right? But in the summer last year, I still had a fully functional torque converter lockup. All of a sudden, in a matter of an hour, I lost the correct lock-up procedure, it was rather random. Maybe the TPS is to blame? Or my whole ECM is shot, its new and is Borg Warner, what I hear is NOT a quality product. Sorry for my random talking, if anybody has ideas let me know. Thanks

 

I seriously doubt the ECM itself is to blame.

Mechanical problems are more common than electronic problems, mechanical things have parts to wear down, get dirty, bind up, break, etc. etc. etc.

You mentioned that the light goes off when you touch the brakes. Also note that whenever the TCC is not locked, the light is off. Thus it's still possible the brake switch is causing your problem, the brake switch could be breaking the circuit as if you had your foot on the brakes, even when you don't.

Does your speedometer work? The computer bases the lockup point (in part) on MPH so if it's not getting the correct MPH reading then it would never lockup. Since your 92 has an electronic speedo, this is helpful info.

Since you have other reason to believe that the CTS sensor may be bad anyways, it's not too bad of a decision to just replace it. You'd be better off to test it first (using the hot/cold resistance check, or ALDL data scan tool) though.

 

Yes, my car has a fully functional speedometer. 91L98Z28 I want to thank you for sticking by this post and helping me out. I have found a pattern to my torque converter's madness tho. It goes like this:

-It won't lock at all when the car is first ran, it needs to be warmed up for like 10 mins at least

-When it does lock up, its usually at speeds around 45 mph, and at periods of less than 1/4 throttle (foot barely touching pedal on a flat or slightly downward surface)

-I have experienced no problem with locking up the torque converter in D (third gear), but then again, I didn't go higher than 55 in D because I dont want to wear the engine.

Hope that info can steer me in the right direction. By the way, how hard is it to change the CTS? How much does it cost, where is it located? Where is the TPS located? How much does that cost to replace and how hard is it to replace. Thanks again.

 

Oh yeah, and how much does the brake switch cost and how hard is it to replace?

 

I don't know how much any of this stuff costs or how easy it is to replace them, I've never had to do it on mine.

I can't imagine either one would be particularly hard or particularly expensive.

You say it works perfectly in D, just not OD?

It's *designed* to not lock up under heavy throttle, or below a certain speed. it's also designed to unlock intentionally for 1-2 seconds when you go from 4th (OD) to 3rd... at least the 90-92 v8's are, I assume your v6 is the same. The trans has an internal 4th gear switch. It's remotely possible that, if your TCC works perfectly in 3rd but intermittent in 4th, that the 4th gear switch is somehow going bad, and telling the computer that you are constantly going from 4th to third and back, making the computer keep the TCC unlocked all the time. You'd need an ALDl data logger to monitor this one, or hook up another test light to that wire of the trans.
I don't really know how else to help you. You still need to do more diagnostic before just going out and replacing parts. Do you have access to an ALDL scanner (like an auto xray, or diacom, or something like that?) Then you could see what the 4th gear switch is doing, and what the computer is commanding the TCC to do, and really isolate the problem. if you plan to keep the car a while and doing your own work, i'd suggest investing in some type of aldl monitoring equipment.

What are the actual clues to you that the TCC is causing problems? Can you feel it going on and off in 4th? The only reason i ask is because if the trans was slipping a lot in 4th it might also feel like the converter was unlocked.

 

Well, when it seems like it is going out of lock-up, it acts like I gave it some gas to pass somebody. The RPMs will quickly shoot to around 2700-3000 rpms, and will be unlocked. The light will turn on when it locks, and off when it unlocks/ is unlocked. Like you said, the torque converter will lock fine in D, but not properly in OD. This could be a bad switch inside my transmission, which means I'd have to drop the whole thing and repair it right? Or does it mean that I'd have to drop the pan and fix it? I have a freeze plug that leaks anti-freeze, maybe that messed up the switch. Well, like you said, its time to get some test equipment, thank you for your help.

 

that is kind of odd if it really does act perfect in D but weird in OD. you might start a new post requestiong dana (probuilt) or transfixleo's help. I don't think it would be a hydraulic problem but maybe.

it could be the 4th gear switch in the trans. to replace it, you'll have to drop the trans pan, but not the whole trans.

When the RPM's jump to 2700-3000 .. where were they before? if the TCC unlocks it should jump no more than 250rpm or so.

freeze plug leaking on the motor won't mess up a switch inside the trans.

 

It actually acts like its going back into third unlocked, but theres no way of telling whether its in fourth gear or third. Ahhhh I give up lol

 

Sure there is. If you are going down the highway in OD, pull the shifter back one into D. If it was in 4th, you'll know it in a hurry. If it was in third, nothing will happen.

Getting back onto track here. if you hooked up a test light, and you feel confident that the test light showed you that the TCC was acting as it was commanded to by the computer, (and also acting incorrectly) then your problem most likely lies with a computer sensor. Beg, borrow, or steal (well maybe not steal) an ALDL scanner and scan that puppy. If you just can't do that, then get out an ohmmeter and at least measure the resistance on the CTS hot and cold and see if it matches spec. If it doesn't, then replace it. After that, the next best guess is the 4th gear pressure swich inside the trans.

Did i mention that an aldl scanner would really be helpful?

 

I came across this site while looking for something else, it may be useful in your situation.

Diagnosing GM Converter Lock-up Problems

 

91L98Z,
You just reminded me of a time that I was on the highway. I pulled the shifter into D when it was not locking, and I jolted forward out of my seat as the car downshifted (not good on my clutch packs ), that tells me that it was in fourth. I will now see what the other guy just posted, "Diagnosing locking torque converter problems", I will let you guys know whats going on.

 

Alright, get this, it's a nice day today and the t tops were off, I'm cruisin down a 50 mph speed limit road, and it locked up when it supposed to, and it held it all the way! It appears the problem has gone away for a while, but for how long