Understanding TCC lockup logic (article on GM's approach) and how to modify it
 

Here is a very good article that outlines how GM's TCC (torque converter lockup) logic and design has changed over the years.

http://www.motor.com/magazine/pdfs/062006_07.pdf

The main reason for posting this is to learn how OEMs do it, so that we can modify our own transmissions to do what we want. Simply adding a TCC lockup switch in may not work. Its also very likely to cause a check engine light on more modern transmissions.

Has anyone installed a TCC lockup switch on a newer vehicle? Even my 1997 Sunfire has a PWM solenoid instead of an on/off solenoid. If I put a switch on, I expect a check engine light.

The four speed auto on my Mazda Tribute (AKA Ford Escape) was an absolute slush box. The car was great except for the transmission and subsequent awful fuel economy. I attempted a manual TC lockup by simply wiring in a switch to ground the lockup solenoid. The solenoid always had 12V on one side and the ECU switched it on the ground side.

It would work for about 3 seconds, until the ECU realized what was going on and put it onto limp home mode, which required a key switch cycle to reset. I do not know whether it went by an unexpected changed in engine vs turbine speed or if it recognized a problem with the electrical circuit. Either way, I didn't try too hard to get it working properly.