Hi,

I recently(3 months) bought a used 2001 Nissan Sentra GXE 1.8L and
since then I was using Super Unleaded fuel and recently changed back
to regular unleaded(i filled my tank some 3 times) and now my Check
Engine light is on since 10 days and i got it checked and they said
the catalytic convertors(front & rear) needs replacement. well the
replacement is costing a lot to me.

Does anybody have any idea that the switching of gas from Super
Unleaded to Unleaded caused this?

Merry Christmas & Happy New Year

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gobonkers_2000 wrote:
take it to one for a second opinion. It would be unusual unless you have
a lot of miles on your '01.

Are you sure you're getting a real diagnosis of the problem or did some
clerk read the code and declare that the catalytic converter is bad?
If the latter, it's highly likely that the problem is not either of the
catalytic converters. Was the code P0420 i.e, catalyst efficiency
below threshold? If so, that does not automatically mean that the cat
is bad. The ECM (i.e. the engine computer) compares the composition of
the exhaust gas going into the front cat with the composition of the
exhaust gas comimg out of the front cat. If it finds them to be
similiar it sets the code P0420 on the assumption that the cat must be
operating poorly if the exhaust gas going in looks just like the gas
coming out. But it determines the composition of the exhaust gas by
monitoring the voltage changes of an oxygen sensor located in the
exhaust stream ahead of the front cat and comparing that voltage
behavior with that of another oxygen sensor located behind the front
cat. So if the front oxygen sensor starts to go bad it may behave
sluggishly resulting in the front and rear oxygen sensors behaving
similiarly and thus setting the code. The fix is replacing the $50
front oxygen sensor, not replacing cats at $1000+.
Using higher octane fuel than recommended is a bad idea. Higher octane
fuel burns more slowly. When used in an engine not designed for it,
over time it tends to leave excessive deposits. Those deposits could
make their way to the catalytic converter and possibly degrade it but
it is more likely that they might foul the front oxygen sensor first.
So if the code is P0420, you need to view the behavior of the oxygen
sensors, particularly, the front one before you can assess what the
problem is.
The switch in gas is probably coincidental but the use of higher octane
fuel over a long period of time may be a causal factor.
I'm not trying to be pessimistic but these days there's far too much
code reading going on and not enough quantitative diagnosis. Hope it
helps. Good luck. Al

gobonkers_2000 wrote:

"JimV" wrote:

It has run approx 70,000 miles.

Thanx for the reply.

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On Sat, 23 Dec 2006 18:25:54 GMT, gobonkers_2000 <none (AT) 000 (DOT) com> graced
this newsgroup with:

Federal emissions warranty requires the manufacturer to warranty the
converter for 8 yrs 80.000 miles on 95 and newer, 5 years or 50,000
miles on 94 and older models.

Don't pay for the replacements. They have to replace them for free.

Here's the link to the EPA regulation:

http://www.epa.gov/otaq/consumer/warr95fs.txt

On Sat, 23 Dec 2006 19:54:08 -0500, max (AT) dontspam (DOT) me graced this
newsgroup with:


oh and btw. No, the higher octane fuel didn't destroy your
converters. No way, no how. *Leaded* gas would, but you're not
using leaded fuel. The percent of octane had no effect on the
function of the converters, much less on three tanks full anyway.