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2001 Cavalier Auto Transmission P0742 Stuck Torque converter Clutch

My girlfriend’s 2001 cavalier has about 160k on it and about a week ago it started shifting harshly accelerating to highway speeds and the CEL came on along with the traction control/abs warning light. I pulled the OBD2 code and it was P0742, Torque Converter Clutch Circuit Stuck On. We took it to the transmission shop down the street the next day and they wanted $600 to diagnose. We called ‘shenanigans’ and decided she should take it to her regular shop. On the drive over the transmission shifted normally. Both shops noticed that the transmission cooler lines were rusty and seeping, but neither thought it was the cause of the problem.

The shifting issue hasn’t recurred even after a couple hundred miles during the week. She hasn’t had the transmission fluid changed and doesn’t know if it had been when she bought it about 80k miles ago. It seems to me that pre-emptively draining the fluid, changing the filter and refilling, especially to check for debris in the fluid, would make sense, especially if it was debris jamming the circuit that caused the error code in the first place.

Anyone with experience with this issue?

I’m sure that the $600 to diagnose involved a teardown of the transmission. Sometimes that’s the only way to really tell what is going on. But - this kind of thing is not seriously an offer to diagnose. Once the thing is out of the car and torn down you either do a full rebuild or put another transmission in it regardless of what is “diagnosed”.

At 160K and with what is probably the original transmission fluid, I wouldn’t blame a shop for not wanting to tinker with it. Its a hair from dead. The thing is well used (160K) and abused (never serviced). Basically, drive it for as long as it will go and then fix it (complete overhaul), get a replacement, or junk the car.

If you’re saying that you would be the one to drop the pan & change the filter I would certainly do that since its just a little time & money. I would also do it a couple of times in quick succession since the pan drop will only get about 30-50% of that nasty old fluid.

If you end up with a new/rebuilt, have the pan dropped/filter changed every 30K miles.

My friend (who just junked his project car and is looking for some wrenching opportunities) and I were figuring we would be able to drain the fluid and replace it and the filter.

My girlfriend doesn’t really like the car, it’s just cheaper to keep it while she’s saving up for a car she’d like.

Have you checked the fluid level with the car on yet? Make sure the car is ON and WARM or else the reading will be higher than it should be. Replacing the tranny fluid in most cars isn’t too hard but it won’t be a true flush unless you replace it by disconnecting the tranny fluid return line from the rad and drain from there. To do this one would have to be pouring fluid into the transmission at roughly the same rate as it is draining from the transmission and one would stop when the fluid appears clean (red). The color of the current fluid is another clue to the state of the internals of the transmission. Does it smell burnt? Does it have metal in it?

Go for it. Its not a hard thing to do - just messy. A basic Haynes manual might be helpful.

No matter what you do, make sure you use the right type transmission fluid - as a GM its probably Dexron VI.

Most of your fluid will still be well past its prime (mostly dead). You best bet would be to then take it somewhere to have a full fluid exchange done - only after the new filter. But that will run you at least $100. The alternative is to do several pan fluid changes in quick succession - each few thousand miles or so. If the transmission has no drain I’d consider adding one. Many warn against that since a lot of them leak, but if you’re smart about it, its unlikely to cause any problem. I put one on my minivan without any trouble and I’m glad I did.

Her shop checked the fluid to confirm the rusty cooling lines weren’t causing a major leak. I haven’t personally.

I was mostly interested in the size and amount of metal debris in the fluid. Granted, I don’t have much to compare it to, but certainly any visible metal debris is probably too much.

Cigroller, what drain did you use? I considered adding one to my tranny fluid pan (my tranny is a chrysler A604) but I didn’t see anyone who makes a drain for it. I was about to just drill a hole, tap it and put in a bolt with a big washer and an o-ring.

I don’t know that it had a brand name - maybe it did. I picked it up from NAPA. Its just a big bolt with the center drilled out and tapped. You pop a .5 inch hole in the pan, bolt goes through with a nylon washer; nut on the other side with a nylon washer; a little blue threadlocker for good measure. Then there’s a smaller drain bolt w/ a rubber o-ring the threads into the middle of the bolt.

It basically looks like this:

If I had a welder (and knew how to weld) I would have just popped a hole & welded a nut to the inside of the pan - bolt & nylon washer on the outside as the plug. If mine ever leaks I’ll probably do that via my brother who has a welder.

It doesn’t take anything fancy.

The transmission is going to need to be torn down. Other things that would cause this is line pressure which is fluctuating rapidly and uncontrollably or a bad PR (Pressure Regulator) valve. The transmission shop was not leading you on.