P2096 is being persistent. (Downstream O2 sensor)

[Cani Lupine]

So my 2014 ES 5 speed has been turning my Service Engine Soon light on with the code P2096, for the downstream O2 sensor detecting lean conditions. Both upstream and downstream sensors have been replaced, but P2096 is still showing up in pending codes even after being cleared twice. Just rolled over 115k miles today.

Before anyone asks, the original catalytic converter IS still there, since I don't feel like dealing with those issues. I do, however, have a ram air setup, but the MAF and MAP sensors are reading fine.

My UltraGauge has been showing the car runs consistently rich by a slight amount, but at WOT the lambda maxes out at .893, even when the commanded AFR is slightly richer. Long-term fuel trim goes between 6 and 3, then up to 7 off throttle.

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.

It's more of an annoyance than anything, since the car runs fine, but I'm trying to figure out the source of the issue. I doubt I'm actually maxing out the injectors from the intake alone.

Anyone else have any experience with this code?

[Cobrajet]

At 190k, I am still on my original cat and sensors. I know people say to change them after a certain mileage, but other people say to keep using them as long as they are not reading out of range. I am going to leave well enough alone.


Did you replace the original sensors with OEM? Some cars are very sensitive to the brand of sensors you install. One truck I had would constantly throw O2 sensor codes with Bosch replacement sensors installed. I switched them out for Densos and the problem went away.

Does your car use any coolant? I have heard that burning coolant can 'poison' the O2 sensors. That said, if your upstream sensor is reading normal and your downstream sensor is reading lean it could very well indicate a problem with your cat.

You have a 'ram air' system? Before doing anything else I would put your intake system back to stock just to eliminate it as a possibility.

[Cani Lupine]

Upstream is Denso, since I couldn't find the OEM NTK in stock. Downstream is new OEM, and the code has been present both before and after the change.

It doesn't leak or burn coolant, thankfully. The level holds steady.

The confusing part is that both sensor readings show slightly rich, but it's throwing a "post catalyst fuel trim system lean" code. It doesn't make any sense, unless maybe I'm maxing out the injectors as it compensates for the intake.

As for the ram air setup, it's been on for quite some time without issue.

[Eggman]

Upstream is Denso, since I couldn't find the OEM NTK in stock. Downstream is new OEM, and the code has been present both before and after the change.

It doesn't leak or burn coolant, thankfully. The level holds steady.

The confusing part is that both sensor readings show slightly rich, but it's throwing a "post catalyst fuel trim system lean" code. It doesn't make any sense, unless maybe I'm maxing out the injectors as it compensates for the intake.

As for the ram air setup, it's been on for quite some time without issue.

A couple of questions for you:
1. Do you suppose you have any wiring problems with your sensors?
2. What other modifications have you made from stock?

[Cani Lupine]

Doesn't seem to be a wiring issue, since everything looked good when I replaced the downstream sensor, and it appears to be operating normally.

Apart from changing spark plugs to NGK Ruthenium and running NGK coil packs, everything else is stock. Those have been in good working order.

I'm wondering if I need to pull the battery terminals and hold the ends together to reset everything and make it re-learn.

My other guess is a leak at the upper flange where the catalytic converter meets the exhaust manifold, and that'll be a huge pain in the tailpipe to deal with.

[7milesout]

My other guess is a leak at the upper flange where the catalytic converter meets the exhaust manifold, and that'll be a huge pain in the tailpipe to deal with.

I was *thinking* maybe there's air getting into your exhaust by way of a leak. As a result, the sensor would detect more unburnt air in the exhaust yielding a "lean" reading.

Have you had that upper flange location loose before? Are there any exhaust locations you've had loose before?

[Cobrajet]

Doesn't seem to be a wiring issue, since everything looked good when I replaced the downstream sensor, and it appears to be operating normally.

Apart from changing spark plugs to NGK Ruthenium and running NGK coil packs, everything else is stock. Those have been in good working order.

I'm wondering if I need to pull the battery terminals and hold the ends together to reset everything and make it re-learn.

My other guess is a leak at the upper flange where the catalytic converter meets the exhaust manifold, and that'll be a huge pain in the tailpipe to deal with.

An exhaust leak is the next thing I was going to suggest.

[flip096]

did your car passed by a flooded street?..it happened to mine a long time ago...my car showed random codes like traction control and P2096 and P1590...it's one of those problems that i didn't figure out and resolved by itself...car never had a problem running...cleared the code after rainy days and never came back...i also noticed you got ultra gauge installed on your car...i also had one before and it throws weird random codes on a random days for 2 years....i unplugged it and never had a problem ever since...

[Cani Lupine]

Alrighty, so I pulled the battery terminals off and held them together to clear out the memory and have it re-learn everything as I drove home from work.

The LTFT settled around 5.4 under cruising, when before it was at 7ish. Lambda is actually showing a bit closer to 1 now than it used to.

However, it now has P0421 in pending, but it hasn't tripped the SES light, yet. P0296 also hasn't come back yet, but I've only driven for 40 miles with two startups.

The confusing thing is that the same multiple conditions can cause both codes (exhaust leak, bad sensors, bad cat, and more). I'm wondering if the upper cat flange may have a leak, but I need to make sure I have new bolts and springs on hand before I try taking it off, as it's my only vehicle.

At least my state doesn't have emissions testing!

[Cani Lupine]

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.