bad o2 sensors?

[bobfo]

hello everyone :)

here is a screen shot of some logged data, do the front 02 sensors look like they are going haywire, or is this normal? Shouldn't they be close to the same as the rear sensors?

thanks in advance

[joecar]

HO2S11, HO2S21 (front sensors) frequently cross the 500mv level in both directions; this is normal and is how the narrow band sensors are designed to operate;
their transfer function has a very steep gradient at stoichiometric AFR and so they overshoot (unless there's a steady state rich or lean condition); the PCM is designed to work with this rapid switching.

H02S12, HO2S22 (rear sensors) flatline at some level; this is normal since they're measuring the operation of the catalytic converters; if these are fluctuating, then the catalyst has failed; I would have expected a leaner voltage for these (0.2 or 0.3 instead of 0.6 or 0.7), but I think it may still be ok.

[leres]

Huh, so it's normal for the secondary O2 output to look lazy. That's sure not what H2OS12 on my Z06 does; most of the time it closely tracks what H2OS11 is doing. I have a log file attached to this post (http://forum.efilive.com/showpost.php?p=52042&postcount=2).

Earlier tonight I made a short log my 2000 Camaro tonight and it looks like bobfo's. I wasn't sure if it was normal because it throws a P0161 (O2S Heater Performance Bank 2 Sensor 2) from time to time. But I think that just means the heater in that sensor is marginal.

What would cause H2OS12 to behave this way? All I can think of is a nice hole in the exhaust, somewhere between H2OS11 and H2OS12.

[joecar]

Huh, so it's normal for the secondary O2 output to look lazy. That's sure not what H2OS12 on my Z06 does; most of the time it closely tracks what H2OS11 is doing. I have a log file attached to this post (http://forum.efilive.com/showpost.php?p=52042&postcount=2).

Earlier tonight I made a short log my 2000 Camaro tonight and it looks like bobfo's. I wasn't sure if it was normal because it throws a P0161 (O2S Heater Performance Bank 2 Sensor 2) from time to time. But I think that just means the heater in that sensor is marginal.

What would cause H2OS12 to behave this way? All I can think of is a nice hole in the exhaust, somewhere between H2OS11 and H2OS12.That log shows HO2S12 tracking HO2S11... if the PCM sees x2 tracking x1, then it throws a converter DTC.

The GM literature shows x2 sensor being "lazy".


The PCM must monitor the three-way catalyst system (TWC) for efficiency. In order to accomplish this, the PCM monitors the pre-catalyst and post-catalyst oxygen sensors. When the TWC is operating properly, the post-catalyst (2) oxygen sensor will have significantly less activity than the pre-catalyst (1) oxygen sensor. The TWC stores oxygen during its normal reduction and oxidation process. The TWC releases oxygen during its normal reduction and oxidation process. The PCM calculates the oxygen storage capacity using the difference between the pre-catalyst and post-catalyst oxygen sensor's voltage levels.<see attachment=""><see attachment="">

http://forum.efilive.com/attachment.php?attachmentid=1931&d=1185805957 (http://forum.efilive.com/attachment.php?attachmentid=1931&d=1185805957)

Whenever the sensor activity of the post-catalyst oxygen sensor (2) nears the sensor activity of the pre-catalyst oxygen sensor (1), the catalyst's efficiency is degraded.


Aftermarket HO2S characteristics may be different from the original equipment manufacturer sensor. This condition can lead to a false pass or to a false fail of the catalyst monitor diagnostic. If an aftermarket catalyst does not contain the same amount of precious metal content as the original part, the correlation between the oxygen storage and the conversion efficiency may be altered enough to set a false DTC.
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[Zfreak]

My sensors look more like the STFT than a normal 02. However they're "oscillating" at a normal amount...just that the "swing" isn't what it should be. I'm looking at the STFT base, correction and multiplier tables to maybe change the swings and keep the 02's alive.....any ideas if that's the right direction?

What gets me is that I can SEE them at .9 at WOT and .005 when in DFCO so its not like they're clogged!

I already bought two new 02's so I don't mind putting them in, but the issue is that I have this problem every few months (like the 02's are getting fouled but I'm convinced that they're not) and its getting annoying.:bash: