According to my shop schematics, there is a mechanical "top gear switch" located in my 700R4. The switch is open when in OD. This circuit is used by the ECM, but what for?

When I replaced my transmission with a rebuilt unit, this switch was not included. I had to ground the wire that would normally go to this switch. Therefore, the ECM never "sees" the tranny in OD. Could this cause any problems?

 

Willie:
The switch is to ensure that it only locks up in 4th gear. It's read by the ECM which control the lockup based on this and other parameters (engine temp etc). If you ground it you will never have lockup. Which as I understand is bad for a 700r4. (gets hot).

Also it's common to have a NC switch in series with the lockup solenoid to un-lock before a 4-3 downshift.
Look at the attached image, switch 1 is the 4th gear switch and 2 is the 4-3 downshift.
(GM have used more than 15 ways of hooking up the TCC, but I believe this is the most common way)

 

Yep, switch #1 above is the one I'm referring to. However, my TC does lock up in D or OD, depending on throttle angle. This has not changed, even before my tranny was replaced. So I'm still a little confused.

Willie