MadVladCivic

Hi guys,
1996 Civic 2dr DX w/ just under 112K miles. Original owner. While driving down the interstate on Fri night, the CEL came on. Pulled over and verified no
oil or coolant catastrophe. No sounds/noises when the CEL came on and engine feels and sounds fine. Idle seems ok and so does acceleration. Took the car
to Advance Auto and they read the code: P0420: Cat operating below threshold.

Background: New Honda dizzy & plug wires Prestolite) less than 500 mi ago; not timed.
Spark plugs (NGK) changed about 18 months ago (less than 5K miles). Car does not leak/burn oil.
Coolant level was normal and appeared normal in color and cooling system operates as it should.
Cat is original. O2 sensors were changed by Honda bout 8yrs ago under a re-call program.

Consulted the service manny, which suggested the issue could result from a bad cat or a bad secondary O2 sensor. The diagnostic flowchart only
allowed for testing a bad cat. Saw several vids at Youtube by ERICTHECARGUY using real-time data on a scan tool to differentiate bad
sensor(s) from a bad cat as well as using a IR thermometer to differentiate a bad cat as well. Is there a way to diagnose a bad secondary O2 sensor?

OK then. What OBD II scan tool is sufficient for this type of work? Have researched Actron CP9670, Innova 3130c, Innova 3040c so far.
Continuous update capability of live data would seem best.
Also, which O2 sensor socket is recommended:
This style: This style:
Have searched the forum and read that sometimes, the P0420 code does NOT mean the cat needs replacing.
Per MAD MIKE. Think it was in the Accord forum.

civic402lx

Any obd2 scan tool will work. I have an ultragauge that i use. Similar to the scangauge2, READ realtime data.
my last car with that code, i reset the ecu to ckear the code. If it came back, at 80miles later for me, clear it again. If it came back again, at the same mile interval. Its your cat converter. Once i replaced the cat converter, code disappear. Never return.

Txdragon

If no code is thrown for a bad O2 sensor, chances are they do not require replacement. Replacing them at that point is simply prophylactic. The trouble code points to the cat, I would honestly start there.

bandit67

Ok, my 2 cents , had this code on my 05 recently, but its cause seems to be the norm on most all the older cars. You have a before and after O2 sensor. You can do a live O2 reading while the motor is running and with good sensors it should show fairly close reading. What the ecm is looking for is a difference in their reading.....which would show that the catalyst converter is working...and doing its thing changing the gases as it passes thru. What seems to happen is the converter gets "dirty" and by that I mean due to higher oil burning, leaking coolant or anything that could change its efficacy from brand new. Maybe ethanol, I don t know, bad gas....the list is prolly much. So, if you reset the code and drive and move the throttle up and down......you prolly won t get the code......but settle on a long set speed , bop, its back. Most folks change O2 sensors first....If that doesn t do it they get a new converter.....which are all only ceramic and are usually junk in a couple of years. Only the stock ones have all the good , high temp , expensive metals in them. On You tube, their are several vids where they run lacuer thinner thru a half tank of gas hoping to burn off that layer of contaminates that may be making the verter not do all it can. Then they remove them and try to clean them with all kinds of cleaners. Nothing I have seen seems to get that unit back to its original state. Some use an extender for the second O2 sensor and that seems to work for them. The code pops when there is NOT a certain amount of difference being reported to the ecm.

EsotericImage

iTrader: (8)

here ya go.. this should "fix" it

MadVladCivic

What exactly does this do? Offsetting the O2 sensor accomplishes what exactly?

MadVladCivic

Hi,

I understand there are least two tests to differentiate a bad cat:
1) O2 sensor readings on a scan tool using live data
2) temp readings on the cat at the inflow and the outflow using an IR thermometer

Basically, the use of an extender immediately suggests two questions (at least):1)

1) Will the extender still allow the vehicle to pass an emissions test? I assume that if the emissions test is conducted solely based
on the readout of a scan tool, which is the case in MD, it would 'fool' the operator and allow the car to pass even if the extender
does not correct the problem w/ the cat.
2) Is it safe for the engine to drive a car w/ a degraded cat, eg, the catalytic matrix has deteriorated/cracked/crumbled allowing particulate
matter to enter the engine itself? Can this particulate matter actually enter the engine via the exhaust manifold? Seems that w/ a "top cat", eg,
the cat is located directly btw/ the exhaust manifold and the header pipe, this would be more of a possibility that w/ a 'cat back' arrangement.

Thanks.

bandit67

I have read from several folks that their cars passed emissions testing with an extender in place. You are correct, no matter how many new or used O2 sensors you put in will not fix or correct a busted, broken, cat converter. I know of no part on a car that does not degrade in time or miles used. If a cat is working at 100% the day the car is sold , what is it doing in six months....99,97%....a year, two years....95%........not sure how much less water vaper it is processing. Once it degrades to a certain level, it will fail emissions testing and I am not sure at what level that is. Is it "safe" to run. Safe for what, the engine does notcare what happins past the O2 sensor as long as exhaust gas is flowing out. I suppose you could take compressed air , and with the engine not running, and with a crumbled cat guts possible blow trash BACK into a cylinder if the exhaust valve was open. Never heard of one sucking trash backwards unless pistons or valves were damaged. Its your car, if it makes you feel better, replace all parts with new stuff. .....peace of mind is good.




5

MadVladCivic

Hi again,

I have some diagnostic tools on order (Innova 3130c scan tool) and an IR thermometer. Always looking for an excuse to buy new tools!
I was planning on testing the cat per the two tests I described in earlier posts in this thread. Depending on the results of those tests, I would
remove the cat and see if is does have particulate matter loosely about. Clean it for ***** n giggles and maybe apply the O2 sensor extender.
That would allow me a little more than a yr to replace the cat before my next emissions test.

MadVladCivic

Hi guys,

I have resolved the issue noted in the thread-opener.
Replaced the cat w/ this: Exhaust Manifold with Integrated Catalytic Converter | Manifold Converter - Not Carb Compliant - Not For Sale - NY - CA | 674-439 | Dorman Products
Ordered from Jet.com and got a 15% discount for being a new customer. Removal of the old cat ran into one rounded nut
problem; otherwise, it went smoothly. Installation of the new cat was quick and painless. Changed all nuts/bolts associated
w/ the cat. Used stainless steel nuts on the exhaust manifold and stainless bolts on the cat mounting bracket. Would have liked
to use stainless nuts on the header pipe but my local h/w store did not carry them and neither did BelMetric. Used copious
quantities of Ni-based anti-seize cmpd. Torqued to spec--or just slightly less than spec.

Erased DTC w/ scan tool. Live data revealed the secondary O2 sensor holding steady readings around .8V. Previously,
it had been all over the place much like the primary O2 sensor. Not sure if there is any benefit to using the IR thermometer
to read temps of gas inflow to and outflow from the cat.

civic402lx

Had one of those. Made my garage stunk everytime i back the car into the garage. Smell of sulfur. Never went away til i replaced it with a magnaflow universal cat. Big different. Even the stock manifold smells bad.