Ok good day everyone. This is my first post so im going to make it as simple but informative as possible.

🚗 1999 Honda Civic Ex Coupe

My transmission went out last year and i took a tranny out of a 2000 Honda Civic Ex and put it into mine. The D4 was flashing which from some research i have learned its a tranny solenoid. My mechanic at the time disconnected the o2 sensor under the car and even though im sure they are not related the D4 went away. Drove it for 8 months like that perfectly until last month i went to a shop to get my brakes and rotors changed. The tech saw my sensor off and put it on then the D4 came back on. The car doesn't have any power in gears. Just drags again like before. Went to a junk yard tested and took 4 different solenoids that go on the tranny and tried them on my civic and still same issue. Changed the cpu and same also changed the battery. Its just there now with this Dr flashing.
HELP