Hello I have a 97 Ford Expedition 5.4L. My check engine light is on and I'm getting a PO 161 code which I look up(O2 sensor heater circuit malfunction bank 2 sensor 2. My question is were is this sensor located. I understand I have 4 O2 sensors.

 

Downstream (furthest from the engine) on the driver's side.

Steve

 

Replaced it today, that fixed the problem, thanks Steve.

 

It sometimes takes days or weeks to run the internal test that makes the needed check to determine if the sensors and heaters are working correctly.

Just a heads-up so you don't get too optimistic too early.

Steve