I have replace my o2 sensor 2 times now and it still is throwing code 5 (oxygen sensor signal) My check engine light only comes on mainly on the highway/freeway at a steady speed/rpm +/- 500rpm.
I use denso o2 sensors and thier direct fit oe ones too. The wiring is all good as well.

I don't know what to do please help....

 

Ever found the issue ?

 

That's a lean situation... you can change the AFM and stop that from happening. I know because I've done it.

 

You have a vacuum leak. DO NOT F- around with the AFM to compensate. Check all of the vacuum motors with a vacuum pump, then grab a cigar and....