O2 v. A/F ?

[Rallytech14]

whats the difference between my downstream O2 sensor and the front O2 sensor, is the front one technically an A/F sensor? idiots at advance auto have me all confused,i only when there because they do free diagnostic scans

this chart makes it seem like the front is an A/F sensor...

http://www.densoaftermarket.com/catalog/catalog.php?part=o2sn

 

[drvsdwz]

the front one is more heat resistant then the rear one, this is why the front one is soo much more expensive. they measure the same thing, just for different control circuits, like the rear one will throw a code for bad cat and the front one adjusts the fueling, like you said(a/f) but it measures oxygen, if there's more o2 it adds more fuel. But yeah the front one is more expensive because it has to withstand more heat

 

[Trainable]

^What he said. The front is also semi-wideband, which adds to its cost, and the rear is narrowband. There really isn't a cheap generic option for the front.