Torque converter locking/unlocking

[Madcat455]

Figured I'd ask this question here, I ran a search but couldn't come up with anything that looked like my issue (they had others mixed in).

Basically, My TC is unlocking randomly at speed... anywhere from 45mph+ with no reason.

I don't have any lights set off at all. It's not shifting wierd and hits and holds OD (if I put it in 3rd, the RPM's are much higher than with the TC unlocked).

From previous posts, I saw that it could be the coolant sensor... but I have a new one with a new T-stat (replaced when I changed the water pump).

Car is a 2000 3.4L with 68K on it.

I've had this issue with other cars and it was allways the TCC Solonoid.... but after searching I'm not so sure it's that with this car (other cars were older and not as computer controlled as this one).

The only thing that made a difference was when I took it to a lube shop to have them check the fluid level. They had it running, and removed a bolt from under the car to check. Said it was full and looked great. After that I had a SES light, but it stopped the unlocking problem. Shut off the car, re started it and the SES light was off (hasn't come back on since) and the problem seemed to be gone for a few days.

but now it's back, and I'm no longer sure of the TCC. Any direction on where to start looking.

Any help is appreciated.

TIA

[ehenaty]

had same problem. Dealer spent thousands, as I bought extended warranty when I bought the car new. A couple weeks ago they finally put a rebuilt tranny in, as they have been tring to fix it for 2 1/3 years. They think it was the torque converter, as there was pieces through out the transmission. They had tried pressure switches and solienods and many other things. Finally runs great and mileage back up.

[xeroinfinity]

Some of these torqu converters are prone to failure.

One other thing, if your MAF or IAT is shorting out(bad wires) your trany will shift funny.

[zeta4]

Originally Posted by Madcat455

Basically, My TC is unlocking randomly at speed... anywhere from 45mph+ with no reason.

My mother's 2001 Alero (49k miles) was doing this between 1500-2000 rpm during normal highway driving. It became so annoying that I took it into the steelership for diagnosis. Long story short, they served up a laundry list of items they wanted to perform to isolate the 'chuggle/fishbite' phenomena totaling about $1300. That's excluding the LIM issue they pointed out as well which would be an additional $875.

I just performed the LIM myself for a total of $200 and replaced the throttle body gasket as part of the plenum cleaning that I conducted while I had the car apart. Guess what? The chuggle/fishbite, surging, unlocking of the TC, whatever its true name/cause has disappeared!! The car shifts smoothly with no hint of surging at speeds between 1500-2000 rpm.

In conclusion, and I can't pinpoint where it was fixed, but somewhere buried in the whole process of the LIM repair this 'chuggle/fishbite' phenomena corrected itself in our case.