Does anyone know the difference between an Air fuel ratio sensor and an oxygen sensor ? I was under the impression that there are two O2 sensors in my exhaust one before cat other after(02 OBW 2.5). So where is this air fuel sensor? And one more question are there 5 speed auto trannys in any of the 2002-2004 Outbacks or are they all EA4T ?

The air fuel ratio sensor is the first O2 sensor (upstream of the cat). The downstream O2 sensor monitors the cat efficiency.

A/F ratio sensor is basically a better (wideband) O2 sensor.

The problem is they seem to fail quicker (at least the bosch ones subaru uses) than you would expect, sometimes without giving a clear error code.