P0139 2008 King Ranch

[reklaw]

As the title states, I have a 2008 King Ranch. I've been getting a P0139 on and off for maybe over a year now. I have reset it and it comes back and I guess I have gone long enough without it that the CEL goes off. Lately, it doesn't go away. Of course I see videos on how to check your O2 sensor with a volt meter and figure I should try and do that before I just replace it. But I have also seen that it could be a fuel rail problem? I have had no drivability problems this entire time so I think it's not a fuel rail issue. This morning when I got to work I hooked up my code reader to look at the live data and it was showing the voltage to be in the correct range and it matched the downstream sensor on the other side. I'm just wondering since the code definition says "slow response" does that mean that the sensor is just going bad and it is just that intermittent and it needs replaced.

There aren't many threads on here with this code so I had to post a separate one. What does everyone think?

 

[Hamfisted]

How many miles on them since they were last replaced ? They're only about $40 apiece from Rock Auto for NTK sensors. The driver's side is pretty easy, the passenger side can be some work.

NTK Oxygen Sensors at Rock Auto






.

 

[reklaw]

I've only had this Expedition for 2 years and I've put about 48k on it so far. About 148k miles total. I don't know if they have ever been replaced.

I did just crawl under it to make sure the wiring and everything looked good and it does. I guess I'm just going to replace it but of course the P0139 is the bank 1 downstream sensor and that's the one that's a pain to get too. Now to figure out the best way to do that.

 

[reklaw]

So, my CEL actually went off on it's own. I still replaced the oxygen sensor and then when I started it up the light was on again. Not sure if it came on in the afternoon before on my drive home or if it came on when I started it after I changed the sensor. I drove it about 50 miles and the light is off again. Hopefully it will stay off so I can get it inspected here in the state of Pennsylvania.

 

[Frank Wilson]

I've had this exact same issue. Light will eventually go off but most of the time I'll just reset it with forscan. I have read that the "downstream" sensor been bad doesn't have any negative effects, but I could be wrong.