civicfan247

on my 99 civic lx my engine light came on so i checked the code and got this PO420 catalyst efficiency below threshold bank1, so i figured it was the o2 sensors so i replaced both and then 1 to 2 days later engine light came back on so i took them off and looked inside at the catalytic converter and it has almost no ware on it at all what else could be wrong ??
also getting bad gas milage

ezone

Throw away the Bosch O2 sensors. Buy the correct OEM NTK or Denso sensors, whichever it had.
You just wasted $400 that could have gone toward the proper repair.
Unless you haven't thrown away your old sensors yet. Reinstall them. Maybe you can still afford the correct repair now.

WTF made you think a P0420 code says replace sensors?




Read this out loud.
Go ahead, I'll wait.
Read it again.
Yes, out loud.
Did you say anything that sounded remotely like "oxygen" or "sensor"???


Do you know how a catalytic converter works? Or even what its job is?
Is Google not turned on yet over there?


Now....Does the car run poorly? Are you sharp enough to realize if it did run poorly?
Exactly what calculated MPG does "bad gas mileage" represent?
Could be perfectly normal for the conditions.
If the engine runs poorly, that must be fixed before attempting to resolve the P0420 code.

BlueEM2

iTrader: (1)

^ Be nice, not everyone is as well versed in cars as you might be. However I do agree that you don't just go throwing expensive parts on the car if you don't know what your doing.

OP, you made the right move in getting the code checked. It's more likely than not your catalytic converter. However, the reason the cat failed might be another underlying problem your car has, or possibly due to old age. This is just a guess at this point, this code can be a whole lot of different things and probably can't be diagnosed over the internet. It sounds to me like it's time to see a reputable mechanic. Here is a quick list I found on the internet by searching:

-Leaded fuel was used where unleaded was called for
-An oxygen sensor is not reading (functioning) properly
-The engine coolant temperature sensor is not working properly
-Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
-Retarded spark timing
-The oxygen sensors in front and behind the converter are reporting too similar of readings

^All these are possible, but my first guess is that your cat has died a slow, horrible death and your spitting out some nasty exhaust and the O2 sensor is saying whooooeeee hold on here something ain't workin.

MelJ

My cat's dead in my car. My MPG and running condition hasn't actually worsened though(probably because it's slowly dying ). I hooked mine up to a scan tool and both my o2 sensor readings were almost exactly the same. I'd say if you had access to one, to use it.

ezone

Sorry. I have to deal with some actual mechanics that have no clue how this all works. It can be very frustrating since I am the one that gets to bail them out after they screw it up and the customer is screaming and out of money. I hate having to undo anothers work, especially when it should have been fixed the first time. They can't learn, or so it seems. Maybe it is because throwing wrong parts is actually more financially lucrative than fixing the problem is.

I also think the very definition of the P0420 code spells out what is wrong. It can't tell you WHY it failed though.


I've had some coffee now, so let me try again:

Leaded fuel poisons the sensors and the cat. Most people can't even get leaded fuel unless it is for off-road or aviation, without going out of the country (Mexico).
CTS with overrich running should have triggered rich codes once the PCM lost control of fuel delivery. I don't think skewed lean would hurt the cat.
Exhaust leaks can skew O2 sensor readings, and also can cause a false cat code. A cracked exh manifold (common) typically causes fuel enrichment that the computer can't control, so that could be a possible cause of a cat failure over an extended time period.
Retarded spark timing should have been a noticeable driveability issue since it should take a timing belt jumping a tooth to make it happen. Yes, it can ruin a cat since fuel delivery is enrichened due to lowered manifold vacuum and late burning. The lack of power should have been apparent though.
O2 sensors giving a similar reading-- is what the PCM bases its judgement of cat efficiency on. It is a symptom, not a cause.

Oil burning/consumption can slowly poison a cat.
Low quality or contaminated fuel can poison a cat.
Misfire can ruin a cat in a matter of minutes.
Time and miles just make a cat inefficient, it eventually loses its ability/capacity to store and release oxygen.
Driving habits can be a huge factor too. Short trips can spell a short life for a cat.


In short, when there is a cat code:
Try to establish the root cause of the failure.
Make sure there are no exhaust leaks between the engine and the cat, and no exhaust leaks for at least 3 feet after the cat.
Make sure the engine runs properly.
Make sure the computer has proper fuel control. (A gas analyzer might be needed to determine this too.)
I also like to give the owner the option of clearing the codes and having them drive it to see if the code comes back, since some conditions that affect a cat can be temporary.
Then pull the trigger on a cat.

Note: Most aftermarket cats don't do as good a job as a factory cat. The computer doesn't like them. If you have to pass an emissions test, you might be money ahead to spend the bucks for the proper cat the first time.
Second choice might be a California CARB/AIR (or whatever) approved cat.


Is this a better answer now?



Whooooeeee, LOL!

BlueEM2

iTrader: (1)

Hahaha yea .. thats a fantastic answer

civicfan247

ok well first of all thanks for the help and secondly i didnt waste 400 $ only 80 $ so thats not a big deal. so it looks like im looking for a crack / leak becasue the inside of my cat looks mint so ya oh and it was only one bocsh and one ntk

ezone

Whatever a visual lookie of the cat makes you think is absolutely no indication of the true condition. All you can see is whether or not it is clogged. It is not clogged.

The computer is the only thing that can judge cat efficiency, not you. The computer has already spoken.

99% of these need the cat when the code comes up.

Get rid of the Bosch sensor.

civicfan247

ok i out the old one back in and so your recomending i get new cat then ??

ezone

If you have checked all the stuff I mentioned in this post: https://www.civicforums.com/forums/2...ml#post4585566
If everything I mentioned is golden, then yes it needs a cat.


HEY, I found this video the other day. Wanna try it and report back if it solves the P0420 code??
http://www.youtube.com/watch?v=5icTm...1&feature=plcp

civicfan247

ok well my grandpa actually just mentioned that about putting camp fuel in at about half a tank and it will clean everthing right up should i try this
and if it does clean it and it does lets say work will the engine light go out ot slef or do i have to reset it ?

ezone

Dude, I thought the video was a joke.
But apparently the guy seriously thinks it works.
The same person also advocates using liquid head gasket, which most professionals regard as a no-no.

So I'm thinking this about the guy in the video:


I have NO IDEA what that stuff would do to fuel injectors, the pump, and any plastic parts of the fuel system. Or if it would adversely affect the internal engine parts.

I just can't be the one to seriously tell you to try it, and I certainly cannot tell someone to try this at work since I am supposed to be the professional at my job. This is not a professional option, IMHO.


I was more interested in hearing about the washing or bathing part of the video though. I figured you had the cat off of the car already so this would be easy.


Autozone and several other parts stores will turn the light off for you. Do that so you know right away if it didn't work.

civicfan247

ya i wasnt jumping in and dumping any of it in but he said he did it all the time back in the day lol umm ya i dont have it off but it can easly be done ill prob do it when i take my tranny out but im pretty busy putting power windows in but ill look into the cleaning or ill take the cat somewhere and they can look into it and i can reset it my slef i have my own code reader its not a big deal

ezone

Just plan on having to replace the cat anyway, and you won't be disappointed.

civicfan247

ok great i appriceate the help and what do yuo reccomend for cats i dont want to spend tons of money but i dont want anthing cheap

ezone

Shorthair cats, because they don't get furballs as bad as longhair cats. Keep fleas away from the cats too, they are hell to get rid of.
Be a responsible pet owner. Spay or Neuter your cat.
Never wash a cat that has all of its claws!


Oh, the car? Take a cordless sawzall to the Wallyworld parking lot and look for a car like yours.....Ummm, scratch that. That's against the law.

I already told what I thought in an earlier post (factory parts) and why. Go back and read it.

BlueEM2

iTrader: (1)

OEM cat = guaranteed win but expensive

You can risk buying an aftermarket cat but its risky business and you may be replacing it again shortly after.