what is a heated oxygen sensor?
 

I have three codes for two oxygen sensors. They mention heated . Is that a special kind of oxygen sensor?

the engine uses 2 kinds of oxygen sensors, non-heated and heated. I wouldn't call it special as all engine makers, not just Nissan, use both kinds. The heated oxygen sensor is after the catalyst. The non-heated is used before the catalyst.

The O2 sensor that is before the catalyst is called the upstream sensor while the O2 sensor after the catalyst is called the downstream sensor.

I thought our Maximas used only heated o2 sensors (positive, negative and reading wires on all of them)? :confused:

IIRC non-heated are typically 1-wire sensors

The two bad ones are three wire, wasn't sure if they meant a special kind instead of three wire. Thank you for the help.! :-)