<table id="post104150" class="tborder" width="100%" align="center" border="0" cellpadding="6" cellspacing="0"><tbody><tr valign="top"><td class="alt1" id="td_post_104150" style="border-right: 1px solid #1C1C1C"> 2003 Expedition Eddie Bauer / 5.4L

My CEL came on with a p0141 code - Sensor bank 1 sensor 2 problem. I picked up a new OEM sensor and put it in yesterday and it seemed like the problem was solved. Today, after say 7 or 8 drive cycles it came back on with the same code. What next?

I was watching the live data on the drive after it came on and it seems to be showing a normal voltage, mostly up around .7-.8v - my b2s2 sensor seem to be consistently maybe .05 or .1 lower. But maybe I'm barking up the wrong tree.

Any ideas?
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Just to be sure you change the correct one...which sensor did you change, driver side, passenger side, before or after the converter?

 

passenger side, after converter.

Thanks!

 

Also - didn't mention before, but it has 52k miles on it.

 

Okay good you replaced the correct one. I had to ask because some people think the driver's side is bank one.

Since replacing the O2 sensor didn't solve the problem, you're now stuck tracing the wiring for the O2 sensor heater circuit to find where the bad connection is. If I had to guess, I would say the break is near the O2 sensor you replaced. My reasoning is that after you replaced the sensor the problem cleared up for a bit. So by disturbing the wiring in that area, or perhaps the connector, you were able to have the problem disappear for a while.

 

Thanks Alloro -

Yeah, this is where I was headed next. It's a real pain in the *** to get to that connector up over top of the transfer box (or whatever that was in the way). I might be able to get my multimeter up there to prod around a bit but it seems to be an intermittent problem anyways so who knows if I'll see anything while I'm there. Should I see voltage across it right away from when the key it's the on position or do i have to start / warm up or anything?

I have a feeling I might need to actually get the wires in my hand up close to really figure out the wiring if that's what it is. Anyone have a better plan to check this wiring out that will keep me sane? A magic hatch I can open to access from above or something? Maybe I can just pull it off whatever is holding it up there but that's likely to cause more problems than it solves.

 

The heater wires are only powered for a short time when the engine is cold. Once things are up to temperature, the heater circuit goes dead and the O2 sensor will then rely on the exhaust heat to keep it warm.

If it were the O2 heater control, or relay, etc. then you would be getting a code for more than just that one O2 sensor. Since it's only that one, your wiring problem is going to be between that O2 sensor and the junction point for the other O2 sensor. I know this isn't going to be a cakewalk, but at least you have a section to focus on.

 

Well it was actually not that bad. As soon as I reached up there and followed the wires back I could feel where the wires had frayed apart and had somehow worn right through the conduit, which I still haven't really figured out (squirrel??). Only one wire was totally severed but a few others were on their way so I doctored it all up and cleared the code and I seem to be good to go.

On the downside while I was under there I discovered I have an oil leak someplace that must be relatively new. My work is never done.

Thanks for your help Alloro!!