Have you checked the code again since you reset the ECU, as it might be an error leftover in the memory from before you changed the sensor. Reset it again and see.
Also, if u start the car immediately after resetting it without turning off ignition, it will go into O2 sensor mode, flashing the checklight on and off, depending on lean or rich, cant remember which way, but you will quickly see if its working when you drive it, after it has warmed up.
note, the pic is of an R34 terminal, S2 stagea is upside down in comparison.