98 Accord Ex running rich

P0420 is typically associated with a Three Way Catalytic
Converter failure or with some type of exhaust leak. First,
was that the only error code? IOW did they also forget to
look for other error codes?

A late model vehicle should not be suffering such failures.
IOW reasons for such failures should also be addressed. How
was gas mileage before these failures were happening? Engine
problem that was dumping too much gasoline into the exhaust
system would then degrade the converter. After all, what does
a converter do? Burn the gasoline that the engine did not.
For example, if gas mileage has always been low (ie low 20s
MPG), then that problem may be why a converter failed.

This is why you have a good dealer. Service mechanics will
have enough experience with these rare failures as to quickly
identify the problem AND locate the reason why that failure
occurred. Because the Autozone man could not tell you this
simple information up front, then assume he is not good enough
to perform any service.

Assume there is something else wrong since a catalytic
converter failure alone just should not occur. Something else
should have contributed to that failure. Too much gasoline
not burned in the engine is bad for converters.

 

Hello all,

I posted earlier with some questions regarding the check enging light that
came on few days ago. I put about 5 gallons of gas on my last stop and it
drove about 90 miles which is terrible. Less than 20 miles a gallon.
Terrible! Anyway, today I went to AutoZone to get the free scan code check
and it turned up P0420. Does anyone know what this code means? The guy at
AutoZone said it might be the O2 sensor. I'm thinking it's either the O2
sensor or the catalytic converter since the car has been running rich for
the past week, and especially noticable in the last couple of days. The
check engine light was reseted today when he tested it, and it hasn't come
on since then. After he checked it, it's been running smooth. No hesitation,
seems it's not running rich anymore, but only time will tell. I'll keep
observing for the next few days and fix whatever needs to be fixed over the
weekend.

Any and all help is welcome and strongly appreciated.

Thank you!

--Viktor

 

According to my manual--PO420-- shows up as
"Catalyst system efficiency below threshold."
I don't know what this means--can anybody else interpret what this means?

 

yea, it means the 02 sensor after the cat indicates that the mixture is too
fuel-rich.... either the 2nd heater 02 circuit is malfunctioning, or (as it
has been mentionned here), the catalytic converter is failing... in wich
case it sucks to be you cuz thats one expensive replacement.

Get a real mechanic to check it out, if it's just the sensor, those should
go for under 80$ (i'm talking about the 2nd O2 sensor, not the first one
located on top of the cat).
It takes about 2 mins to install one, but you need to warm up the engine
first a bit, since the catalytic converter expands when warm and makes
installation easier.

If you need to replace the converter, thats anywhere from 170 - 400 $ right
there, depending on the model ....

These are, of course, prices for OEM or good brands ....
Bosch, etc...

ANd you're right, if the code is lit - this indicates to the ECU that there
is a malfunciton with the censor, which in turn disables the real-time fuel
control... which is made to allow for optimum fuel /air ratio (something
that the 02 sensor monitors).

In case of trouble, the car runs in open-loop mode, i.e. it reads data from
fuel injection tables... regardless of weither it makes for a healthy
fuel/air mixture... thus your car is "running rich".

Hope any of this was helpful

peace out

 

Tom and Nelson, thanks for your speedy replies.

The gentleman at AutoZone tried looking for additional codes, but that's the
only one he got. The car is 6 years old, which is not exactly late model,
but I follow you on that one. It's got 99K miles on it. I ran in the mid
30's per gallon couple weeks back. Now it runs below 20. My understanding is
that cold air causes more gas to be burned due to more oxygen coming in
because of compression in cold weather conditions. The loss in gas economy
is usually 10% which is about 3-4miles per gallon, and I've lost 15 or so.
That's not normal.

If someone has any other suggestions, please speak up.

Thanks!

--Viktor

 

Yea, right on the money

However, don't dispair.... I personally think that your problem lies with
the cat, but thats just me.
HOWEVER, thats goodnews, regardless of what you may think. Only the 1st O2
sensor's data is used for the fuel/air mixture adjustement, the 2nd one only
monitors the efficiency of the catalytic converter. The dumb thing is, if
either of the sensors set a code, the engine might still be running in
open-loop mode (that is, lotsa gaz.... bad mileage).

It is techincally not dangerous (unless you're a green peace freak) to run
with a failing converter or a malfunctioning 2nd 02 sensor, as long as the
1st one (the one on top of the cat is working fine).

Here's the deal : there's a way to trick the ECU into thinking that the 2nd
02 sensor is working normally, even if it's busted or not even there. You
need to basically have the 02 output voltage in the right range (around 0.45
volts), and trick the heating circuit into thinking there's "something to
heat" - by shorting the terminal 3 and 4 of the connector with a resistor.
I'm a bit busy right now with school and whatnot, but this weekend when I
got some time, i'll design this thing for ya (its very basic, nothing but
resistors and capacitors) so you can try to plug it in, instead of the o2
sensor - for peace of mind Again, this would only work for the 2nd
sensor, the primary sensor is essential to good vehicle operation.

 

Hello Yuri,

Thanks for the informative reply.

So basically, if the O2 sensor is damaged, even if the engine and the rest
of the emission system is OK, it would still run rich because there's no
appropriate feedback from the O2 sensor, am I getting this right? So if the
second O2 sensor is the problem, then replacing it will get the car back to
running normal, right?

I pray to God it's not the catalytic converter because I'm a little low on
the money right now. The second O2 sensor is $83 and the first one is $109
at AutoZone. That's not too bad compared to a new catalytic converter, as
you said running in the few hundreds' range.

If anyone has more information they'd like to offer, I'm listening.

Thanks!

--Viktor

 

Once again thanks Yuri! Can't wait to check out your design. Very
interesting

And again, more information is welcome

Thank you all!

--Viktor

 

Viktor,
I read all of the interesting posts on this subject. It appears that some
of the posters believe that you have a bad sensor instead of a problem
with the catalytic converter. I just wanted to add that at this point in
time, you don't know for sure whether the problem is with the catalytic
converter or the sensor. You might want to check out the warranty
information that came with your vehicle. It's possible that your catalytic
converter might still be covered--I'm just guessing. I suggest that you
have your vehicle checked by a mechanic that you trust to determine
whether the catalytic converter or the sensor is the source of the
problem. This is especially true if your state requires a pollution or
emission test each year.

 

If the Oxygen sensor was bad, then that code number (was it
P0137?) would have also appeared. Diagnostic procedure for
the 'bad converter' code says to also verify for additional
codes such as a 'bad oxygen sensor code'. According to
Autoworld, no such code existed. Therefore, an O2 sensor
failure is not a likely reason for this problem. Furthermore,
O2 sensor failures occur without creating a 'bad TWC' code.
Whatever has failed had to make gas mixture richer than a
failed O2 sensor would have.

One additional point. Newsgroups are about information
exchange. Please reply to this thread when a solution is
found.

 

Hello Tom and Nelson,

The car was running yesterday afternoon and today. It's been running fine
after the scanner reset the ECU. (Does the code scanner reset the ECU or
just the error code?)

Can you recommend good mechanics? Firestone is a ripoff. I don't know how
good of a job they do but their prices are outragous. I'm not stepping a
foot in there. The other day they asked for $400+ for a set of 4 tires for
my accord. Couple more hundred and I might as well buy another car.

Anyway, if I find something, I'll let you all know.

THanks!

--Viktor

 

The best way to find a great mechanic is to talk to your co-workers and
friends. At least one or more of them will tell you about a mechanic
that is great. The Honda dealership has excellent mechanincs but you
would have to pay much more to them than you would pay to local mechanics
which is why lots of people don't take their cars to Honda dealerships for
service unless they have newer cars still under warranty.

Of course, the rich people will go to the Honda dealership but most of us
are not part of that group--especially me.

 

I know those discount mechanics. One Honda had valves
adjusted so badly to be loosened by more than 12 times (more
than one full turn) what valve life would be in the entire car
life. Engine made a terrible racket after adjustment and yet
that discount mechanic (and his supervisor) did not even hear
it. They were into costs; not value.

Heater core control wire pulled off and not properly
installed so that heater output constantly even when air
conditioner was on. Disc brake rotor resurfaced improperly so
that vibration damaged wheel bearings. Or bearing was
defective and discount mechanic never bothered to check -
therefore resurfacing disc rotor wrong. Either way, problem
directly traceable to man who costs less because he is not
good enough. Problem that cost that owner $hundreds more even
after returning to the discount mechanic and demanding those
discount brakes be replaced with Honda brake pads - for free.
More than three trips because job was first done discount.

Even dust cover (so that disc caliber slides clean and easy)
never reconnected so that caliber seized due to brake dust. I
found that major problem. Muffler replaced with a Midas brand
that failed within 20 to 40% of a normal muffler life. Timing
done improperly (discount mechanic did not know about a
required jumper - so even gas mileage was significantly
lower). Readjusting timing cost more money.

You don't save money by being a 'bean counter'. Such
mentality is why GM cars cost more to build than Mercedes -
comparatively equipped. GM buys on price - not value - which
is why their costs are higher. If you don't like the car,
then go to those discount mechanics.

Talking to co-workers is only good if the co-worker has
technical knowledge. Does he do his own service? And even
after that co-worker recommendation, the service man must
still pass muster. Too many males don't know beans about cars
- only recommend the man who talks pretty - what some call
'acting cool'.

Sit in dealer; listening to how they talk to women. The bad
service rep will outrightly lie about technicals because she
is a woman and therefore must be dumb. Yes, I saw one Honda
dealer blame the woman because mechanic did not put oil filter
on correctly. Even the parts dept guy there considered retail
part sales a nuisance. Co-worker recommendations are only
good enough to begin a search. Many males don't learn an
engineering mentality - the need for irrefutable technical
facts - because they don't do some work themselves. Instead,
many males can only judge based upon personal chemistry.

Why do I use the dealer? Because therefore service even
solves problems before they happen. Less hands (and smarter
hands) inside the car means less failures. You are talking
too much like a GM mentality - who therefore thinks numerous
service visits are necessary. I have seen it too often
because I never need all those return visits. I learned why
dealer mechanics can be so important.

BTW, I also have another independent mechanic because he is
local. He costs just as much. He does the little things like
inspection. He has demonstrated great knowledge which is why
his higher prices actually cost me less.

Another 'save money' technique. Many don't buy their wiper
blades from the dealer. Therefore inferior rubber in discount
Autoworld blades require replacement every three months. Pay
a dollar or two more for Honda blades and get more than 12
months- virtually no streaking. Pay a little more and get
more than 4 times the wiper life. Therefore again, save big
time. Real world: Trico, etc discount wiper blades are for
those with a GM mentality who foolishly wish they were saving
money.

Honda owners are richer because they don't cost control -
and therefore spend less money on maintenance and other
things. That Autoworld service man who read your Pxxx code
should have all but been yelling in your ear, "Run now if you
want to save money!"

I am not an auto mechanic. Just that those discount
mechanics are too often so bad that even I had to locate and
fix their bad workmanship. Expensive Honda dealer mechanics
often mean you spend less money - which is why you bought the
Honda in the first place.

Example: dust in a valve (a small hole in plastic) that
slowly opens EGR valve. Explained the problem and Pxxx code
to service man. He and his mechanic look at each other and
immediately cite that plastic valve. A discount mechanics
would have uselessly replaced a $70+ EGR valve (plus labor)
because that is what code said. A smart mechanic immediately
knew it was that $4 plastic valve. Immediately obvious these
guys knew their stuff - which is why they cost more per hour
and save me money.

 

Hi Tom,

I completely understand and agree with you. Of course that's if you are in
the workforce earning money. At the moment I'm still spending money :/ in
educating myself (college) so I try to be smart in choosing my mechanics.
Honda dealer is too expensive for my situation, and a lot of the discount
mechanics do a half-assed job. It's best if you have some knowledge to know
wether the mechanic is taking you for a spin or if he really knows his
stuff. I also find it fun, challenging, and healthy to work on my car while
learning and relating new knowledge to everyday life.

There are bad mechanics everywhere, even in dealerships, and even the good
mechanics make mistakes at times. For me it's important the customer
satisfaction for a period of time instead of a one or two mistakes that the
mechanic might have made. Sometimes the saying "you get what you paid for"
is a bunch of balloney but there's a definite relation in most cases.

--Viktor

 

Much to be learned by experience and mistakes. Often one
need not take it to a discount mechanic. One should be doing
much service personally. Money is not saved in 'dollars per
hour' but it does save money overall. And 'doing it yourself'
teaches things necessary to differentiate good mechanics from
bad. And yes, also a 'fun' to it. For example, fluid changes
should never require even a discount mechanic.

To save money, a Honda shop manual is a given necessity
(even though manual is not as educational as even 15 years
ago).