(Aus) 08 Holden V8 Caprice: 6L80E transmission problems

[CapriceV8]

The transmission in my V8 Caprice with 6L80E has a problem, symtoms as follows:

When cold, everything seems fine (edit: except for the slightly rough shifts from 2nd to 3rd, mentioned below)
When the transmission sump temperature reaches about 266F, it sticks in 2nd and, I think, 3rd gears. Sometimes it will shift, but only if I rev it much higher than I normally would have to. Other times it will not shift at all. (tried manual mode) It drives normally when stuck in gear - no flare that I can detect etc.
Sometimes, before I notice any problems when driving normally (in D), I will try manually shifting to 2nd or 3rd when the car is stationary. This normally works fine, but when the temp is approaching 266, it will refuse to shift out of 1st gear. However, if I then take off in D normally, it does seem to drive normally. So, this refusal to shift in manual mode seems to be a sign that problems are about to start.
It will sometimes throw error code P0716 ("Input/Turbine Speed Sensor Circuit Range/Performance"). It only ever throws this error when the car is stationary. (and it will shift to 3rd gear, which I understand means it is in limp-home mode).

Now, I've been doing something which I fear may have contributed to the problem. In order to reproduce an engine pinging problem, I have been revving the engine a bit (typically a bit over 1000rpm) in gear, holding the car with the brakes. (it didn't ping when revved in neutral) It never reported an error when I did this, but perhaps it still caused some damage.

If the transmission does overheat, does it report an error?

History:
Vehicle has about 155,000mi on the clock.
The transmission was rebuilt about 31000mi/12 months ago, including a replacement of the transmission computer. (they told me it was just a bad solenoid, but that the solenoids can't be replaced individually, so they have to change the entire computer - unlike the old days)
A day or so after the rebuild, that same error code (P0716) occurred, again when stationary, in D. The mechanic replaced the speed sensor, and that error never occurred again until recently. I didn't look at the temperature when this occurred, but I remember that it was after a fairly long drive on the freeway without stopping. Note that another very mild problem did (and still does) occur very intermittently though - shifts from 2nd to 3rd would be a bit rough, when taking off gently.

Current work done to date:
The same transmission specliast that did the rebuild has replaced the same speed sensor for a SECOND time. I have not tested it yet, but I will be amazed if this fixes the problem. (will be testing it out shortly) (the rebuild is out of warranty btw)

Any assistance much appreciated.

Greg.

[Crazy Paul]

http://www.grrrr8.net/crazypaul/P0716.pdf

http://www.grrrr8.net/crazypaul/Spee...put%20Test.pdf

[TailG8er]

Also make sure the fluid is not low and even overfill a little.

[GM Customer Service]

Greetings Greg,

Truly sorry to hear about the engine concerns. Have you thought about taking it to a certified dealer for an official diagnosis?

William R.
GM Customer Care

[CapriceV8]

Thanks William - I may do that.

A bit more info. As I said before, the input turbine speed sensor has been changed (again), but the problem is still there - it is reluctant to change up, requiring higher revs than normal. It has not thrown the P0716 error (or any errors) yet though. It still happens when the trans. sump temperature gets to about 130 deg C.

According to this: http://www.atraonline.com/gears/2008.../2008_1_34.pdf the TCM is thermally protected at 144 deg C. Assuming that the TCM is normally at approximately the same temperature as the sump(?), this suggests to me that my transmission IS getting too hot, because the ambient temperature here has been around 15 to 20 deg C. In summer, the sump temperature would presumably rise by 20+ deg C, which would then put it over the thermal cutout temperature of the TCM.

The transmission was serviced at the same time as the sensor was replaced. They said that the fluid looked to be in good condition. (I presume they would have told me if the level was low - I'm assuming that the level was ok)

Just btw, I have a new (12 months old) 3.6L V6 Caprice now as well - it has the 6L50 transmission. Anyway, the maximum temperature I've seen in this car is a bit over 100 deg C so far. Quite a bit cooler. Being a smaller engine and a lighter duty transmission though, I'm not sure how valid it is to compare the two.

Greg.

[G8-4-Speed]

If it is reading 266, that is over-temp condition where is uses different shift patterns and strategy. There is no reason for that transmission to run that hot. Either it is a faulty temp sensor on the TCM or there is a cooler/converter/trans problem.

[CapriceV8]

Yes, it was definitely running too hot. It has now been repaired. They said that the transmission section of the radiator was blocked, AND the torque converter was also overheating. They replaced the radiator and the torque converter. I've thoroughly tested it and I am satisfied that the problem has been rectified.

Greg.