Dear P0141, Lets break up.

Hi all!

I'm new here so I don't even know where to start!

I own a 1997 expedition. SHES MY BABY!
About 2 months ago I started having an issue with code P0141!
I changed both downstream 02 sensors and a few miles later the code popped again!
I changed the sensors again, and what do ya know? The code popped again. I set up and appt at the mechanic. He said he checked all wiring and swapped out my Bosh sensors (that I had just put in) for Fisher ones and "my CEL light went off by its self". So I paid their ridiculous fee and went on my way. On my way home.... CEL light came on for the same P0141 code!

I took it to my dads house. He told me to replace my back Cats. Which I did. 160 miles later...P0141 came to visit me again!
My dad found out my head gaskets were leaking. I dropped it off at his house. He did my heads, redid my whole exhaust, shocks, ect ect. After 2 days of him driving it.... P0141 came back to say hello. He's checked all of the wiring over again and all of the wiring looks fine. He's switched sensors from passenger to driver, ect. After dumping $500 into my vehicle, I'm ready to pull my hair out.

PLEASE tell me someone here has had this same problem?!?

Welcome to the site, I would suggest finding someone who can perform real diagnosis instead of tossing parts. Not digging your dad, there is a procedure to be followed when diagnosing problems. You don't just look at wiring, what is the starting voltage? What is the voltage at the connector? Is there a good path back to ground?
Since you are in PA, you have salted roads in winter raising hell with wiring. Did he check and clean grounds?

http://www.obd-codes.com/p0141

After reading the above info you will notice the trouble is in the heater side of the sensor and not the part that senses the oxygen content of the exhaust. If you are willing to bust your knuckles a little we can guide you through the process of locating the problem.

At this point I just want her fixed so I'm willing to do anything. I keep getting different "cross your fingers and hope it works" fixes. But I'm not ready to throw in the towel just yet!

That's the thing. I've taken it to mechanics and they can't even figure it out. I've done live scans on the sensors and they are volting even bank 1 sensor 2 is volting (slow) but volting.

The mechanic also said he checked all wiring and it all looks fine as well. Sometimes it takes me driving 6 miles for the CEL to come back on with the P0141 code and sometimes it takes 160miles for the CEL to come back on.

Seems the more time the truck has to idle (city driving) the faster the code pops. As long as I'm steady driving (highway) it doesn't come on.

Does the live scan monitor the heater circuit of the O2 sensor or just the output voltage from the sensor that measures the oxygen content?
Get the wiring diagrams for the engine and check resistance on the affected heater circuit.

Just the output. And for that sensor to even start putting out I have to literally sit there revving the engine for a good while...

It probably starts responding 5-10minutes after the other 3 sensors have been responding.

And that could probably be caused by not being up to operating temperature. Which explains the code......
I'm closing the other threads you have started - better to use one thread.

Right. Okay, so I've traced the wires as far as I can (some of the wires are up over the transmission which make them impossible to get to) and the wiring I've seen and looked at look fine, the sockets where the sensors plug into look fine. My exhaust have been completely ripped apart and re welded to seal up any leaks it might have had, head gaskets been replaced.... So where do I go from here?

Can you tell if your battery is dead just by looking at it or if a wire is broken internally? If you can please let me in on the secret. You check wiring or anything electrical on the vehicle with a multimeter or dmm(digital multimeter).

You need to get the wiring diagrams so that you can trace the circuits, identify which wire's you are dealing with and measure the resistance of the wires.

Then you verify voltage at the plug for the O2 sensor to make sure it is the same as battery voltage.

Okay, so here's another tad bit of info for me to pick your brain about. Last year, I blew my motor. The dealer I bought the expedition from replaced my motor. The only paperwork I got from the work was the bill (go figure). Since last year the dealership has been sold and bought and all old employees have been fired. When I've started dealing with this issue (P0141) and looking up wiring diagrams, all of the wiring diagrams I can find all show 4 wires for the sensors...

My sensors and plugs ins only have 3 wires?

And of course the dealership has "no old paperwork" to tell me exactly what motor was swapped into my expedition.

Plugs and sensors should be 4 wire. Post pics of what you have. If the pic size is too large you will need to use a hosting site.