I am having a strange issue. I have an o2 sensor error on Sensor 1 bank 1 so I was stupid and got a cheap one off Amazon. I put it in, cleared the error code and drove around for a while. The code came back. I figured it was because of the cheap sensor so I bought a Denso sensor and put it in this weekend. Now I am getting the same code again. Is there a ground for these things somewhere I shook lose when I did my HG job or something like that? I am at a loss. I know it is not working because I am getting HORRIBLE gas mileage. Any help would be appreciated.

2003, 4.6. 156,XXX miles

 

Could be so many reasons but I had same issue
the connector sometimes gets gummed up or wires not in properly
also if you have a bad fuel purge valve and sticks open you dump vapours and in my case it made engine run like crap and throws the bank 1 sensor 1 code

also a good smoke test to make sure you don’t have vacuum and exhaust leaks

 

only use walker brand o2 sensors in a disco. they're not the cheapest ones but they're usually cheaper than bosch, and they seem to be the most reliable.
do you have a code reader that will show you live data from the sensor?