# Scan tool O2 sensor B1 S1 voltage readings? What's normal.



## jjr57 (Sep 17, 2018)

I just recently purchased a scan tool, the generic type that is supposed to work with all OBD-II compliant vehicles,*to read the various 'live data' streams from my2010 Jetta with the 2.5 engine* When I check out the rear oxygen sensor (B1 S2) it reads in the normal .01 to 1.00 volt range.* However when I select the front oxygen sensor (B1 S1) it comes up showing mili-volts for that one.* Does anyone know if this is normal, and if it is, what would be the expected readings for the front sensor?* Thanks in advance for any help.


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## Ichabod0525 (Feb 11, 2018)

the expected range in closed loop is 0.1v to 0.9v can also be written as 100mv to 900mv. See if that clears things up a bit.


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## jjr57 (Sep 17, 2018)

Ichabod0525 said:


> the expected range in closed loop is 0.1v to 0.9v can also be written as 100mv to 900mv. See if that clears things up a bit.


Thank you. I have since discovered that the B1 S1 sensor on a lot of vehicles today are Air/Fuel Sensors and they are different in how they behave vs. the traditional B1 S2 sensor. The rear sensor, S2, reports voltage in the manner you described. The front sensor, S1, can report in several different ways depending on the manufacturer. In the case of VW they report in miiiamps where 0 indicates a short of some kind. In order to completely diagnose the proper behavior of the front sensor short term fuel trim has to be monitored as well.


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