Hi Everyone,
My 1999 Accord, 2.4 VTECH, 124K miles just started to show a 0420 fault - Catalyst efficiency low, or similar.
Has anyone seen and corrected this, short of replacing the catalytic converter?
No related faults for O2 sensors.

 

Do a search for P0420. There have been numerous threads on this subject.

In summary, look carefully for any intake or exhaust leaks, and if possible check the pre-cat O2 sensor for correct operation. If all these look good, a new catalytic converter is likely fix. OEM is best, but very expensive.

good luck

 

I had the same code on my 98 Accord as well. I changed the 02 sensor and I'm been driving without a problem. The code did not come back. Its been about 2 1/2 months since and 4000 miles

 

Ultimetly, if the pre O2 sensor is not telling the engine to deliver the proper amount of fuel, the cat cannot work properly and the post O2 will set this code. If the engine itself is not working properly and it is too rich or too lean then the same thing will happen. The cat has to operate in a cerain range, it cant clean up a huge mess (gross poluter), the rest of the system, engine has to help some too. If you need a cat, only buy a Honda OEM. Same for a pre O2 sensor.

 

It is not an o2 sensor. If it was an o2 sensor the code would be "P013_"
P0420 is a cat code NOT an o2 sensor code. At least according to the honda techs on this website. You need to buy another cat or try the defouler trick to temporarily fix the problem. Eventually you are going to need another cat.

ajluu - you have only been 4000 miles. Your code will more than likelycome on again. Unless the Honda Techs on here don't know what they are talking about since they don't do this for a living or anything.

 

Indeed it isn't an O2 sensor code, however a defective (perhapsslow response) O2 sensor might cause this code to set w/o setting an O2 sensor code. You should check the fuel delivery system carefully before purchasing a $500-$1000 OEM catalytic converter. A bad fuel pressure regulator, leaky fuel injector, or verydirty air filter might also cause P0420.

P0420 can also be caused by intake air leak or exhaust leak (allows air to enter exhaust when inside presssure is subambient).

I spent about 6 months testing and retesting my 99 Subaru Forester w/ P0420 for above faults before finally replacing the catalytic converter. I used an aftermarket Eastern Catalytic converter, and so far have been pleased. Post-cat O2 sensor performance is slow steady voltages, mostly around 0.7 volts.

good luck

 

You are right about that Texas. I didn't mean to tell them to throw parts at it. I know that's what it sounded like.
Everyone needs to test test test test before spending money.

 

A 1999 accord with a p0420??? Put a cat on it. That's what honda recomends on em. Their the last ones to tell you to throw parts at a car.

 

Testing a cat is an art all its own, but as I said, if the cat does not get the close to correct gasses into it, then it cant clean them up. Its not ALWAYS the cats fault. A gross polluter will set a P0420 with a good cat. Yes, in this case the cat could be the problem, I would want to see a 5 gas reading though, if they are not gross, then a cat it is.

 

Thank you all for your answers. The Honda manual does not detail a lot on this fault, other than the decel test and Co2, and their solution is cat replacement.
I was thinking that the O2 sensor responses will have to do with it, since ECU reads some input/output differential to tell the cat condition.
What has happened though, the light went off and I just realized that I used o bottle of fuel cleaner just the day before light coming on. Hell of a coincidence - open for speculation.