Re: 1998 O2 sensor

[garwillis@msn.com (Garfield Willis)]

On Tue, 6 Jun 2000 15:14:51 -0400, "Bruce Plecan" <nacelp@bright.net>
wrote:

>I can't answer your specific question but I can say that in some
>applications there is a specific delay in which the ecm/pcm expects to see a
>response to a change in mixture, when doing the code 44/45 test in some
>applications.

Yes, I believe this would be used in the diag procedure for the
*pre-cat* sensors. On the post-cat tests, the sensors are usually biased
outside the range they'd achieve when lit off (this to check for a
southbound sensor), and then the diags watch for them to come into the
expected *around stoich* range, and then change very little. One thing I
DON'T know for sure is if they have any MINIMUM signal swing they look
for; I kinda doubt it tho, since a perfectly operating cat gives very
little signal change in the post-cat O2 sensor. I believe all that's
going on is to make sure they (post-cat sensors) don't swing OUTSIDE a
MAXIMUM signal swing, but again this test would ONLY be applied during
closed loop with no AEs underway.

I spose if the diag writers were REALLY clever/smart/anal (your choice
:), they could LOOK for an excursion when you have an
enrichment/enleanment underway or go open-loop with major power, cuz
then the cat is EXPECTED to be outta the picture, and then the post-cat
sensor IS going to move outside the stoich band.

And of course, you can expect the post-cat to also show significantly
lean when fuel is cut during throttle-off, but again, this wouldn't
violate the test, because the post-cat sensor wouldn't be checked during
this time. Only during stable closed-loop.

Gar


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