Help with P0325 (Knock Sensor) and P0135(O2 sensor heater circuit) codes ka24de

[300sx]

I've searched and nothing helped. I scanned it maybe 6 months ago when the CEL first came on and gave me those codes. Cleared it and it went away for about 2 months. It came back so I just left it on without clearing the code and it went off after a couple days. About a month ago it came back on and it stayed on. Even clearing it, it came on after a few minutes of the car being on. So I went ahead and replaced the knock sensor (PITA!!) and the O2 sensor. After putting the new O2 sensor in i started the car, let it idle for a few minutes then scanned it. P0135 went away but P0325 remained. So I left it cuz I did not want to mess with the knocksensor anymore. Took it for a drive, pulled into the garage and ran the OBDII reader, hell!! P0135 came back up.

What do i need to do in order to clear these two codes?