A/F sensor

[john s]

So, with great hesitation, I made a trip to the dealership to diagnose a "check engine light " only to find that after searching for a location of this a/f sensor that I am puzzled. Is the a/f sensor the same as an O2 sensor? The youtube vds seems to point to this. I own a 2003 outback with 2.5 and the vids I've looked at are not helpful in finding the location if this is indeed a separate sensor.

[Numbchux]

Typically referred to as an Oxygen sensor, and listed that way in aftermarket listings.

But an Air/Fuel sensor (Or wideband) sensor can detect a wider range of mixtures with more accuracy than an Oxygen sensor. Modern cars (in the last 20 years or so) generally use AF sensors upstream to monitor the fuel mixtures and adjust how the engine is running, and just O2 sensors downstream just to monitor converter functionality.

[john s]

Thank You for that clarification. The videos I was watching used the term interchangeably and showed the location at the front of the engine between block and radiator. got me confused (the error code was p0030).I appreciate your input

[Numbchux]

Yep, the term is frequently used interchangeably.

The front one on a 2003 2.5 is installed right in front of the first cat, angled up along the RH side of the front of the transmission.

[GeneralDisorder]

Air Fuel Ratio sensors are also called "Wideband Oxygen Sensors". The classic "Oxygen Sensor" or Narrow Band Oxygen Sensor can only read 14.7 air fuel ratio - or rather it can only tell you if you are above or below 14.7 AFR and they produce an output between 0 volts and 1 volt with 0.5 volts being exactly 14.7 

WBO2's have a variety of ranges and specifications but are distinct in that they produce positive or negative current (in milliamps) indicating direction and amplitude away from 14.7 AFR. This is often converted by the engine computer or another control module into either digital CANBUS data or a 0-5v analog signal. 

GD