Speed Sensor trouble

[dherrera83]

I have a 96 Infiniti J30 and check engine came on a few weeks ago and as if it was a curse i need to go pass emissions and the OBD2 says its the speed sensor but I have changed it and still no luck it came on about 30 min after I replaced it . Now questions I had and needed help on, does this car have just one sensor on the transmission or is there an input and output sensor located where i can work on it . Thank you in advance for your help.