I received this code a little over a week ago however it has not returned once I reset the ECU a little over a week ago... should I still replace it? Why would it come on in the first place if it might be still good? The O2 sensor code came on simultaneously with the EGR Hi Low Flow system code.

 

It's the 0702 or 0703 code correct?

I have both of those the CEL came on just as I rolled 156K. I now have 163K and the light hasn't come back on, but the codes are still there. I will be replacing both O2 sensors soon.