Oxygen Sensor and Code 1 CRX SI

I just did a DX to SI manifold swap on my CRX and everything worked well except the O2 sensor went out and Code 1 on the ECU. I replaced the sensor and reset the ECU but a few days later, same problems. I'm thinking it could be the $45.00 O2 sensor from Checker so I am replacing with the OEM $200.00 in a few days. Before I do this, does anyone know if the problem could be somewhere else causing the code ?

that probably is the problem. I bought mine from autozone (i think it was a bosch) and the dealer told me that they have different readings and so on, so i just bought an OEM one.