I use to run with premix ..... not so much anymore.
The MM tune I have has the oil metering pump adjusted.

 

I installed the new Rear O2 sensor this morning and have been able to put a few drive cycles on to it.
So far so good no cell

 

I had the same code as yours today...P0138 02 Circuit High Voltage ( Bank1, Sensor 2 )..so maybe my sensor gone bad...where u get your Rear O2 Sensor?

 

I ordered it from the local Mazda dealership.

They are not that expensive ... 130ish IIRC

 

Oh I might add that you should check your CAT.
The Rear O2 sensors job is to measure the cat efficiency it is possible its not broken and your cat is screwed

 

Right now, she's still running smooth...I'm going to check the cat if its glowing red after giving her a spin...is there any other method to check the cat?

 

Disassemble my friend
You need to have a look at it

 

no one mentioned you gotta make sure the car is properly warmed up for the etest. I refuse to to wait for a test and always warm up my car pre test.

Even my 13 year old (at the time) cutlass with over 250,000kms passed

 

For emissions it also helps to change your oil and filter. Dirty oil will trip you up..

 

Really?
Where are you getting this from?
Link?