need help fixing codes P0325 & P0151:

[chadl]

Check engine light has been on for a couple days now and I had to bring it in for an emissions test--obviously it failed and these are the reasons why:

P0325: Knock Sensor 1 Circuit (Bank 1 or Single Sensor)

P0151: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)

Does anybody know what to do??

It's an Xterra SE if that makes any difference.

Thanks!!

[OffroadX]

Ignore the knock sensor code, it's not critical and will not show up on its own.
02 sensor is the upper one on the driver's side.
The service manual says a problem with any of the following could trigger the code:
Front heated oxygen sensor
Front heated oxygen sensor heater
Fuel pressure
Injectors
Intake air leaks

What year is your X?

[chadl]

02'

I had the dealership fix the O2 sensor and everythings cool now. It was under warranty (I have an extended one up to 100k)

Thanks.