Check Engine Light - O2 Sensor

[SwampTrac]

Well I was driving down the road yesterday and my check engine light came on. Its never been on before, so I drove to O'Reilly and had them do a scan. They pulled a code P0136, which indicates a bad O2 circuit in Bank 1, Sensor 2. Luckily my county no longer requires emissions tests, so I'm not in hurry. But I dont want to hurt my fuel economy as this is my daily driver. Does anyone know where this sensor is exactly? How difficult is it to replace? Also what brand should I go with?

 

[Todd Z]

Sadly this could be MANY things from a vacuum leak, to a bad injector, to a burnt wire to many other things. Replacing the sensor is normally not the issue.

 

[cadman777]

When I got that code on my '03 XLT, it turned out to be leaking intake plenum seals.
The way I discovered that is by 'smoking' it with my home-made smoke tester.
That's before the Chinese made affordable smoke testers that you can get on fleaBay.
While I was in there I replaced the Thermostat housing.
Back then, there were no aftermarket aluminum ones, so I just went with Motorcraft.
Also, while in there I changed all the other o-rings and seals on the top end, along with doing a tune-up (cap, wires, plugs) and vacuum lines, pcv valve, timing chain tensioners, etc.
It's been running like a champ ever since (except for now, a decade later, the timing chain cassettes are going bad!).

 

[SwampTrac]

Thank yall for the input. Actually the check engine light turned off after a couple days, and it hasnt been on since. Maybe just a fluke? If it comes back on ill probably just ignore it, since tracking down these issues takes more time than im willing to spend.