Jose L Santos

I have a 99 Honda Odyssey and I just install a 2001transmission from the junkyard. It was fine for about a week. Suddenly it start going slow and rougth shifting. I stop wait half hour and start the vehicle put it on drive and my transmission was on neutral mode. I check the fluid was a lil over ffill.i try to drain a lil fluid by the cooling line, no fluid was coming out. I put the scanner and is giving me P0720. I check the resistem with a mltimeter and I am not getting the mandatory 5v. How do I fix that problem to start getting the 5v.I didnt flush the cooling on the radiator when I install the new transmission. I would like to know what the soluction When not Getting the mandatory 5v on the countershaft speed sensor. And if that is why my transmission not engaging into gears? Thank you in advance for any responds