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Can the Catalytic code P0420 be overridden permanently?

106K views 149 replies 47 participants last post by  kgardonia 
#1 ·
Put on your thinking caps here people. I am about to ask a very deep question. From what I am told, the P0420 code says that the Cat is "bad". I believe that it is only slightly out of the tight tolerances that Honda has set for it.

What makes the code go off? Is it an increase in resistance through some wire screwed into a sensor on the cat? Possibly a decrease in resistance? What makes it go off?

I want to override this at the source and do away with this completely. Does anyone know of a way to fool the computer into thinking everything is OK? There must be some way other than having to spend more money on a perfectly running van, especially in these tight times.

Anyone know how??
 
#2 ·
You can just ignore it as long as you don't have to pass any emission testing. It would be hard to trick the computer. It's looking for differnt data readings at different running conditions.
 
#3 · (Edited)
No, unfortunately you can't just unplug the O2 sensor and substitute a resistor, it's a bit more complicated than that (you can still do that if you want to drive around w/o an active explosive device right in front of your face, and don't want the airbag light on, however).

The following link helps explain why that code is getting set and how to know exactly for sure whether it is your cat or the O2 sensor(s) that may be the root cause issue:

http://www.troublecodes.net/articles/catfailure/

For off-road use or diagnostic purposes only ;) , there is also something known as an oxygen sensor simulator--google this phrase and start reading!

My van has had this issue, intermittently, since I bought it a few months ago (former owner did mention it, but light was off when I purchased it). I have cleared it twice using a friend's SnapOn ($$$) scanner, and a few times it has cleared itself. I've got another two years before my next emissions test, so I'll get more serious about doing something about it a few months prior to the test.

If you do just drive it with the light on, it is a good idea to get the codes scanned a few times a year, just to make sure that no other problems have developed that you may not realize.
 
#4 ·
The PCM needs to see a slower switch rate from the downstream sensors as compared to the upstreams. Basically, the downstreamers should see less hydrocarbons, more oxygen and therefore put out a lower voltage than the upstreamers. The PCM compares this ratio and will set the P0420 if the minimum isn't met. This particular 'test' won't even be performed if one of the downstream sensors doesn't pass their own operational tests. I have seen "cheaters" avail. online, but have no idea how they work since they have to work in conjunction with the upstream sensors.

Joel
 
#6 ·
I recall seeing a thread here or elsewhere that one could put some extensions on the O2 sensor, to pull it back out of the exhaust flow and make it less sensitive. Looked like a pretty easy change.
 
#7 ·
SuperDad said:
I recall seeing a thread here or elsewhere that one could put some extensions on the O2 sensor, to pull it back out of the exhaust flow and make it less sensitive. Looked like a pretty easy change.
I also found that in my search and have applied it and willl see if it works. The CEL is currently off :)
 
#8 ·
MikeT125 said:
I also found that in my search and have applied it and willl see if it works. The CEL is currently off :)
I think you've solved the "light" annoyance at this point. The O2 simulators are used with CAT test pipes (either hollowed out real CATs or just a staight pipe section fabricated) for off road purposes only....

:duh:
 
#11 ·
chiody said:
I think you've solved the "light" annoyance at this point.
:duh:
I realize that although the light is now out, that the cat still isn't running at 100% efficiency. I am guessing that it is running just a little off that but not enough to effect performance or my mileage. If the cat was becoming clogged, or another problem was surfacing, the mileage would start dropping and it hasn't. We have been getting 21-24 mpg for a long time now and that is where it always has been.
 
#13 ·
chiody said:
As you mentioned, the code indicates the CAT is running a bit hot but due to strict ranges, it may be far from permanent damage. Just monitor it for further codes and hope they stay off. If you have real problems, they'll come back on real soon.
Agreed. Also, the little mod I did is not permanent and does not disable the CEL so it is free to throw any other code it needs to.
 
#100 ·
I performed this "upgrade" on my 2000 over 1-1/2 yrs ago and the light hasn't come back on with the P0420 code since. Over 20k in mileage since then. Have done this 4 different times on Odysseys and it seems to work good.


Official S2000 HOW TO / DIY - Honda-Tech
Just did this with the 42009 non foulers and it worked perfectly. Need to find out more about the potential down side to this modification is.
 
#15 ·
CARMandP said:
I performed this "upgrade" on my 2000 over 1-1/2 yrs ago and the light hasn't come back on with the P0420 code since. Over 20k in mileage since then. Have done this 4 different times on Odysseys and it seems to work good.


http://www.honda-tech.com/showthread.php?t=2162522
I performed this "upgrade" too and it worked great! No more dreaded P0420! Total cost is $8 for the non foulers plus $10 for an oxygen sensor socket. I think the hardest part of the whole process is drilling the non fouler clamped by locking pliers (I was stepping on the pliers the whole time to stabilize it as I don't have a bench vise... :p)
 
#16 ·
I went right home and did this. My van aced NC emissions, but is still throwing P0420.

So I went right home and did the nonfouler mod (in good conscience)

It takes about 30 miles to come back on, so we'll know real soon.
 
#17 ·
rrhartjr said:
I went right home and did this. My van aced NC emissions, but is still throwing P0420.

So I went right home and did the nonfouler mod (in good conscience)

It takes about 30 miles to come back on, so we'll know real soon.
I was in a similar situation, my odyssey passed California emissions nicely despite throwing the P0420 intermittently, so I did this in good conscience too. It just didn't make sense to me to spend so much money for a new oem cat.
 
#18 ·
paulgoh said:
I was in a similar situation, my odyssey passed California emissions nicely despite throwing the P0420 intermittently, so I did this in good conscience too. It just didn't make sense to me to spend so much money for a new oem cat.
Yea, if these vans are passing CA emissions, how strict are Honda's standards?!
 
#21 ·
Re: is anybody replacing the cat as well?

I am expecting this trouble code fairly soon on our van given the age (2000 EX with 125K miles) and was wondering if anyone who has had success with this mod has also replaced their OEM cat with an aftermarket one (DEC or Bosal or whatever) and still been able to avoid the cat trouble code permanently.

Naturally, if I can just do this little fix and keep driving merrily with my original cat that would be great, but it would be nice to know if this fix will avoid the CEL if in fact I end up replacing the original cat with a DEC.

Thanks for the input guys.
 
#23 ·
Sensor "Upgrade" Are you still keen on it?

CarMandP,

I've read your October 2007 post about how you often use spark plug non-foulers to distance the O2 sensor from the exhaust stream and stop Ody vans from throwing the P0420 code. I am interested to see if you have continued to do this modification and if you're still happy with the result.

I have a 2001 Ody LX with 104,000 miles that has just started throwing the P0420 code.

My wife, when on a trip with her sister recently, had a mechanic in North Carolina diagnose the issue. His recommendation was replacement of the Catalytic Converter.

From what I've read, it seems that Honda's standards for the exhaust gasses are exceedingly stringent...to a fault. Doing your mod seems like a simple fix. I like it!

Thanks,

The General
 
#24 ·
Re: Sensor "Upgrade" Are you still keen on it?

General said:
CarMandP,

I've read your October 2007 post about how you often use spark plug non-foulers to distance the O2 sensor from the exhaust stream and stop Ody vans from throwing the P0420 code. I am interested to see if you have continued to do this modification and if you're still happy with the result.

I have a 2001 Ody LX with 104,000 miles that has just started throwing the P0420 code.

My wife, when on a trip with her sister recently, had a mechanic in North Carolina diagnose the issue. His recommendation was replacement of the Catalytic Converter.

From what I've read, it seems that Honda's standards for the exhaust gasses are exceedingly stringent...to a fault. Doing your mod seems like a simple fix. I like it!

Thanks,

The General
I did mine almost a year ago and it's still working great. No problems with the van, no problems passing inspection.

Is P0420 the only code your van is throwing at the moment? The cat degradation is usually triggered by the frequent EGR problems these vehicles have.

Make sure you get the EGR problems corrected if present to prevent the cat from degrading further.
 
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