Check engine light came on a couple of weeks ago w/p0740 code. I had had the tranny flushed @ Monro about a week before that. Took it back over there and had them check it and asked if the flush might have caused some dirt to get into the solinoid and they said no. They hooked it up to a computer and it is showing that the sol circut is open. I've noticed that when it seems to downshift from 3rd to 2nd the tranny bangs sometimes and overdrive disengaged the other day while on the interstate doing about 65/70mph. Overdrive is ok again but I have not had it over about 62mph. Any idea's as to what might be going on here and if I might ruin the tranny by driving it like this? Thank's

 

OK ....First welcome to CF

Now .....P0740 can be a little tough to diag without the use of a scanner. Basicllly the TCC Solenoid is malfunctioning. Using the scanner you can test the TCC (Torque Convertor Clutch) Solenoid and narrow down the cause to that solenoid or the 3-4 Shift Solenoid.. That being said, changing the fluid and filter will not cause either of these conditions to occur on it's own, but I have seen where the wires to the clucth back had been dislodged or damaged while doing the service.
I hope this helps you.

 

Before doing anything else, pull and clean the NSS.