P2096 is being persistent. (Downstream O2 sensor)

[Eggman]

Theory:

So, this depends on how exactly the code is triggered. It specifically mentions long-term fuel trim, so now it has me wondering.

I'm thinking that the old O2 sensor was failing and showing the car was running leaner than it actually was, and thus falsely raising the enrichment in the long term fuel trim enough to trigger the warning. After replacing the sensor, the long-term trim was still highly enriched, thus keeping the code in place.

After pulling the battery, it reset the long term fuel trim to zero. This caused the catalytic converter to not properly work during warmup for the first cold start, triggering the pending code.

I reset the code this morning, so we'll see if it comes back.

One thing to note is that it was running REALLY well when enriched after replacing the rear sensor, with more pep than after pulling the battery terminals.

That’s interesting information. It seems to suggest that there might be some ECU reset or relearn procedure that needs to be done after replacing oxygen sensors.

[7milesout]

Cani Lupine - I have a lot of respect for your theorizing. However, I have my doubts about your theories. I don't think they hold water.

I tend to believe, in this case, there is 1 solid root cause to this problem. By solid I mean, it is something definite ... like an exhaust leak (for example). O2 sensors, in my experience, tend to get "lazy" and get noticed by the ECU as "bad." They don't tend to become inaccurate, as much as just slow.

I think there's one exact thing, and it remains hidden from discovery (as yet). But I think you will excavate the issue. Maybe some actual smart guys on here will help (actual as in, I'm not one of them).


7milesout

[Cani Lupine]

One thing im curious about, though, is that I'm only seeing a lambda range of 0.893-1.325 on the UltraGauge, even though the manual says it's range is 0-1.999. obviously, I'm not going to get air/fuel ratios that extreme, but it won't go lower than 0.893 even when commanded richer.

I'm not sure if I'm maxing out the fuel injectors, or if it's just something odd with the way the UltraGauge reads the wideband sensor. I might have to get a different diagnostic tool for that.

[Cani Lupine]

A couple days after the hard reset and clearing the P0421 once, and no codes have come back, so I it looks like you do need to pull the battery after getting P2096 to reset the LTFT.

Also, I found something interesting when looking into the fact the wideband lambda won't go richer than 0.893:

[Cani Lupine]

It's baaaaaaack!

Check Engine light came on during hour 2 of a 3 hour drive, P2096 again. Just a bit before, I noted the car was feeling quite good after a nice pull from a red light. I did notice that at least once during that trip, the combined short and long term fuel trims jumped up to 11 for a bit.

Clearing the code won't get it to stop coming up in pending, so I'll have to look for another cause. :/

[mohammad]

After some research, it looks like the downstream O2 sensor voltage is running high. It bounces around from 0.58-0.74, sometimes as high as 0.88, and I read somewhere it was supposed to be at around .45 volts.

Based on this website https://dannysengineportal.com/o2-ox...ptoms-testing/ a voltage of .8 would be rich and .45 would be ideal

Have you checked the obvious thing to see if the spring loaded connection between the engine and the catalytic converter is leaking?

Also, have you checked that the sensor reference voltage is correct and stable under various conditions? could be old wiring that shorts when vibrated maybe or under high engine electrical load? if it were to short to ground i think that would give you a lean condition right?

[klroger]

Remember, the downstream sensor is measuring Cat efficiency, not so much engine operation. What are you're voltages if you compare the upstream & down stream sensors?? Do they look the same when in closed loop, or is the voltage steady in the downstream sensor with the upstream one cycling between rich & lean???

[Cani Lupine]

Okay, so it definitely is an exhaust leak. Had a buddy plug up the tailpipe and it was still running normally, and I could smell the exhaust in the engine bay.

It looks like it's coming from the bottom flange, since I don't feel anything coming from the manifold or upper flange, and there's smoke coming up from past the cat when the tailpipe is blocked.

[7milesout]

See post #6 and bow before me!

[Cani Lupine]

It was indeed the simplest answer, but it wasn't in the spot I was expecting.

Unfortunately, the parts are going to be dealer only, since I can't find them anywhere else.