Auto Parts: Oxygen sensor, honda crv, fuel mileage

Question
I own 2000 Honda CRV. Car has 138000 km. In August on way home from trip engine light came up. I checked code and it was P 0131, primary O2 low volt. Dealer told me that I need new sensor. I asked if they can check the old one that we know that sensor is the problem. They said,that they don't check them. I bought Haynes repair manual and there is instruction how to do it. I didn't try it yet, instead I erased code to see if it comes back. It happened in October almost exactly two months apart. It happen on trip 100 km long. I reset code again and so far nothing happen. My question is, if sensor is bad it will take two months to do it again? I bought new one and I am ready to replace it,but I want to be sure that sensor is the problem.
I bought BOSCH direct replacement sensor 13539. Dealer told me that I have to use Honda sensors only. I asked them who is making sensors for Honda and they didn't know. I am sure That Honda have somebody to make sensors for them. I think Denso.What would be your steps to fix this problem.
Thank you,
Roman Sindelar

Answer
I would go ahead and replace the sensor. The code for the low voltage is an internal problem with the sensor. It is very common. Plus it is time to replace. They do get old and carboned up over time. You should notice a slight increase in performance and fuel mileage also.