1996 Tranny ?

My brother-in-lows tranny just stop going into overdrive, it’s a 1996 DeVille, 4.6 Liter, 131000 miles. This started about 2 weeks ago, since then he had trans fluid and filter changed but it did not help. Someone told him it was the OD solenoid and its inside the trans and you had to take the trans apart to fix it. Does anyone know if it is in the trans and if there is some way to check and see if that is the problem.
Thanks
Joe

No easy answer here, the trans has to be scanned with a trans function scanner ot look at the pcm commands and solenoid functions/ slippage errors.

I think you are talking about the torque convertor clutch solenoid. And yes, that is inside the transmission. That only locks the torque converter when the trans in in 4th gear. Is it going into 4th gear?

I think you are talking about the torque convertor clutch solenoid. And yes, that is inside the transmission. That only locks the torque converter when the trans in in 4th gear. Is it going into 4th gear?

Na, does not go into 4th gear ( overdrive ) My brother-in-law is taking it to the caddy dealer today.