I found my solution on the "net". Apparently if the oxygen reading
at the fore and aft sensors is the same, it means that the converter
is not efficiently cleaning the exhaust fumes and likely needs to be
replaced, resulting in the check engine light.
Replacing the sensors probably wasnt necessary in the first place.
Wish Id known that B-4 I did it.
> I have a '00 Legacy GT and changed both oxygen sensors after
> getting a Check engine code P0420 (i think) for oxygen
> sensors. Within a week the check engine light is back- same
> code. Why would new sensors, fore and aft not keep that "check
> engine" light off?
Yeah, I tried to explain that in an earlier thread on this ng, but folks see
that $1400 tab for a set of converters and their eyes glaze over. Suddenly
the cheaper O2 sensors look a lot better. Oh well look on the bright side.
If you haven't changed the O2 sensors before, you were due for them anyway.
It's because the PO420 code doesn't have anything to do with the O2 sensors
per se. That code sets when the sensors determine through correlation that
the catalytic converter is not doing it's job. If the O2 sensors themselves
have a problem it sets a completely different code(s).
here's a related but slightly different question: i do not get a cel,
but if i hook up a code reader, the "c" test (cat. converter) always
flashes, indicating that it didn't complete. this has been going on
for months (well over 100 "trips"), and with no (apparent) ill effects.
what does this mean?
'02 legacy wagon, 5mt, 168,000 km
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