O2 sensors pre- and post-cat

Mark Romans romans at pacbell.net
Fri Sep 11 03:58:27 GMT 1998


Hi Bruce:  At the GMTC they say the post cat o2 sensor is watching for
change.  If you start getting changes in the 02 level then the cat isn't
working.  Remember the OBD2 system is set up to watch for system
degradation.  So the post cat 02 is there to monitor the effectiveness of
the cat.  That's it.  I don't know if they set up any cute routines to check
it.  But it was explained to me that it is watching for change.
Mark
-----Original Message-----
From: Bruce Plecan <nacelp at bright.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, September 10, 1998 6:20 PM
Subject: Re: O2 sensors pre- and post-cat


>
>-----Original Message-----
>From: xxalexx at ix.netcom.com <xxalexx at ix.netcom.com>
>To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>Date: Thursday, September 10, 1998 9:06 PM
>Subject: Re: O2 sensors pre- and post-cat
>
>
>
>> If standard O2 sensors only work at a single O2 %, and the cat itself is
>changing the O2 concentration in the exhaust stream, and the ECU is cycling
>the pre-cat sonsor around its optimum ratio, then what does an ECU expect
>the post-cat sensor to be telling it?
>>
>If you happen to see a 96 or later GM manual they give graphs and
>limits and operation.  The ECU expects the CAT to release O2 at
>a frequency. every 1 or 2 min?  If CAT does not put out enough O2
>and car has less than 100,000 miles go to dealer and get a free new one.
>alex
>
>I been starring at the EK, and Y 97 manuals all day today, what areas were
>they in emissions/diagnostics?.  I can't find them.
>Bruce
>




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