2012 OB , 2017 Impreza
On most scanners, the O2 sensors are labelled "S1" and "S2". (not to be confused with "bank" 1 and 2)
- S1= upstream
- S2= downstream
The AIRFLOW sensor is the MAF sensor. (Mass AirFlow) It usually measures in grams/second (g/s)I have all these O2 readings and cannot for the life of me figure out which is the actual O2 vs. the upstream Fuel/air sensors.