my check engine light came on and the reader said o2 sensor bank 1 sensor 1 which sensor is that exactly??? someone help

 

That would be your primary O2 sensor. What year/model/trim do you have, so I can tell you where it's located?

 

primary sensor is normally in header, right??

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nvynuke18 &raquo;</TD></TR><TR><TD CLASS="quote">primary sensor is normally in header, right??</TD></TR></TABLE>

Yes, but in some models, they are both in the exhaust manifold.