It is the O2 sensor. Your cat may now be ruined as well from getting too
rich a mixture put through it. Dont just replace the cat, fix the problem
then fix the cat.
KH

"Mike M" > wrote in message
.. .
> My son's 89 6 cyl.Cherokee just barely failed the Ca. smog test. It
> passed the 15 MPH but failed at 25 MPH on the "NO(PPM)" part of the test
> (max allowed is 875 PPM.his read 1066 PPM). Anyone have any ideas what
> the problem might be?
> The mechanic told him it is probably either the O2 sensor or the
> catalytic converter.
> TIA
> --
> "Trust me, I do this all the time"
> Mike M
>