SBUBandit said:
Well, doing a little reading and getting my learn on, and found an interesting site. This is intended for older Vettes, but explains how the 4l60e TCC works and determines when to lock up. About halfway down this page there is a nice graph that shows it is a combination of throttle position %, gear, and speed.
How To: 4L60/65E trans tuning. Shifting/TCC/TM (w/ Pics) - LS1GTO.com Forums
Keep in mind, the above link is to help folks understand the questions that are asked when requesting a "tune" from a 3rd party supplier. The link, may, or may not, correctly describe the factory operation of the 4L60 trans.
The overdrive/converter lockup is pretty straight forward for the factory 4L60e.
The PCM will step the transmission up the gears (1st to 4th) as the road speed and engine speed increase. The only way the driver can stop this process is to move the shift lever to a lower gear number, such as 3. The trans will not shift into 4th if the shift lever is at gear 3.
The torque converter clutch locks in 4th gear (when D is selected) when the engine reaches a certain temperature. and power is not being called for (as in passing, or climbing a steep hill). The above is also true when 3rd gear is selected on the shift console.
In other words, if the engine is warm, and you are not asking for passing, or climbing, power, the converter clutch is locked.