P0420 Code - Oxygen Sensor connection

jkp · Dec 18, 2005

I've had this P0420 code for a month, so I have been researching it quite a bit.....Here's my theory....If anyone can confirm or refute it I would appreciate it.
If you get the P0420 code it is probably your oxygen sensor, and not the catalytic converter. (caveat....assumes your fuel economy is normal)
If your O2 sensor system gets way out of whack, your engine can run in "closed loop" mode, which means that the O2 sensors are not controlling fuel/air mixture, and your fuel induction system defaults to rich....under these conditions, damage to your catalytic converter can follow.
Since my fuel economy is excellent 26 highway, 19 city average...I am concluding that I am not running rich, and therefore probably no damage to the catalytic converter....furthermore, I have read several technical articles explaining the functioning of O2 sensors and recommending their replacement at 100k (Odyssey)
JKP

William Wiles · Dec 18, 2005

Until they are analyzed with an OBD2 testor all your theorys are just plain guesses. There are several tests done by the computer for the O2 sensor to determine if it is bad. If you get P0420 with no other codes chances are better than 90% the converter is bad. EGR could have some affect on it also and I would give it more ao a chance than the O2 sensor. Have it analyzed on an OBD2 testor instead of throwing parts at it on a wag........

Year and Mileage would help in the WAGing

jpit · Dec 18, 2005

I agree with William_Wiles. Have it diagnosed correctly. Most likely the cat is the problem. I'm also a firm believer that the EGR valves/ clogging problem leads to premature cat replacement.

The Honda TSB 03-073 that the Honda service guys use tells them to replace the cat for a DTC P0420 so that's what they will do. Cats are covered under 8/80K miles warranty.

jkp · Dec 19, 2005

W Wiles, and Jpit
Thanks for the input.....a few reasons that I am skeptical re: re placing the catalytic converter...first, I have seen several posts in this forum where Odyssey owners have had their catalytic converters replaced at Honda dealerships and elsewhere, and the P0420 code comes back....second, catalytic converters should last for the life of the car, unless you have some significant or long term engine malfunction which shortens its service life, or perhaps for folks that have snowy winters, maybe corrosion from road salt could neccesitate an early replacement. One more; I guess I am predisposed to be suspicious of just about everything the Odyssey OBD tells me. As you and everyone else that owns an Odyssey knows, there are many "bugs" in this vehicle's OBD electrical/sensor architecture.
My 99 Odyssey just passed 100 K.
I certainly don't want to "throw parts at the problem on a wag"...thats why I am looking into it here.
JKP

2000LX_VT · Dec 19, 2005

Interesting twist...

About 2 weeks ago my Ody wouldnt start. I spent about 5 minutes straight trying to get it to turn over, and it wouldnt. I know 5 minutes is excessive but it was below freezing and I thought that maybe the cold was a factor.

After getting the Odyssey towed back to my house, I inspected the drivers side fuse panel to see that I had broken off the 15Amp "IG COIL" fuse, most likely with my foot while engaging the parking brake. I replaced the fuse and was back on the road instantly. About a day later the CHECK ENGINE light came on. I pulled the codes and I got the same P0420 code. I started wondering if my excessive starting attempts had somehow flooded the system with gas, or caused the cat failure. I figured that I too would start with the sensor and go from there, as cats are supposed to be for life. So I've driven it for about 1.5 weeks with the Check Engine light on, then sometime on Saturday, while we were driving around, it just shut off and hasn't come back. Anyone seen this? I thought the only way to get it to shut off was to clear the codes, which I did not do. Could the problem have worked itself out? The fuel economy was definitely worse, significantly, I haven't been able to monitor it since the light went off though. I guess that would be the test.

William Wiles · Dec 19, 2005

Most codes will reset after several drive cycles with no failure condition. Your assumptions about the converter being overloaded could be correct as it also takes several drive cycles to set it.

jkp Most of your statements about the obd2 system are incorrect. Don't have time to explain all of them now as I have to pick up my wife as it is snowing about 4 inches an hour right now......

William Wiles · Dec 19, 2005

jkp said:
W Wiles, and Jpit
Thanks for the input.....a few reasons that I am skeptical re: re placing the catalytic converter...first, I have seen several posts in this forum where Odyssey owners have had their catalytic converters replaced at Honda dealerships and elsewhere, and the P0420 code comes back....second, catalytic converters should last for the life of the car, unless you have some significant or long term engine malfunction which shortens its service life, or perhaps for folks that have snowy winters, maybe corrosion from road salt could neccesitate an early replacement. One more; I guess I am predisposed to be suspicious of just about everything the Odyssey OBD tells me. As you and everyone else that owns an Odyssey knows, there are many "bugs" in this vehicle's OBD electrical/sensor architecture.
My 99 Odyssey just passed 100 K.
I certainly don't want to "throw parts at the problem on a wag"...thats why I am looking into it here.
JKP

jkp First taking everything you read in a user forum as gospel is dangerous. Yes there have been one or two people that have replaced the converter with an oem that they say failed. Usually because only the p0420 code was addressed. The Odyssey has a high voluum engine so a lot of third party converters do not have enough catalyst in them to work with the ODY. Analyzing the switching rate, voltage and switching speed of the O2 sensors will show that.

Catalytic converters will not last the life of the van. Catalyst material will degrade over time with use. I believe the current estimate is they should last 100k miles. The only way cold winters will affect it is pumping more fuel through it because of cold starts and short trips.

As for the OBD2 system being flawed I would like to know where you get that from. I have been working with the OBD2 system on my Ody and other cars since I bought it two and a half years ago and have found nothing flawed in it at all. The only flaw is that Honda as all car manufacturers won't release all the proprietary data that can be scanned so there is a lot of data we can't see. Maybe the high cost units have more but they are out of my reach. Several people on this forum have stated the p0420 code is set too soon but a scan of the sensors will show the code is correct as the converter is not doing it's job. At the same time if the converter is to be replaced the other systems should be chacked to ensure they are working correctly. The codes and failure points are dictated by the EPA.

I hope this post doesn't offend you but I feel a lot of what you posted is false and if read by several people two orthree will take it as gospel and propogate it as fact.

jpit · Dec 19, 2005

jkp, I don't think that there are a lot of bugs in the OBD2 system on the ODY. I do think that the OBD2 'senses' a few problems that are genuine at the time of failure. As William_wiles indicated in the last post, after several OBD2 drive cycles if the problem that originally set the Diagnostic Trouble Code is no longer there then the 'check engine light' is turned off. That would be the correc way for it to be handled.

For your P0420 code there are a number of reasons why it can be set. The downstream O2 sensor is the item that determines whether your catalytic converter is efficient. It's rarely the 'cause' of the P0420. It's only job is to 'sense' a deteriorating catalytic converter. I won't go into how it does it as you may have read about it anyway. Occasionally this sensor does fail but not as often as the upstream O2 sensor whose job it is to feedback the Air/Fuel ratio to the PCM.

I have an O2 eliminator on my downstream O2 sensor so I don't get the P0420 anymore but that's a whole different story.

jkp · Dec 20, 2005

W Wiles
Hey I'm not offended at all...I am just trying to figure this stuff out, and I appreciate knowledgable folks such as yourself weighing in. As to the service life of the catalytic converter, I have done some more reading, and I'd now agree with you on the 100 K....having had two older Accords (third gen, 5th gen) that have surpassed 200 k and are still going strong w/annual emissions tesing) without ever replacing a cat, I made the leap of logic that they should last. I guess that the issue here is increasingly more and more stringent emissions standards.
I am glad to hear your confidence in the OBD system on the Odyssey,...I would not say I'm convinced, but I certainly am rethinking much of what I thought I knew about this problem.
I am not taking anything I read in here as gospel, that is why I am posting to this forum...you know even if I was a certified Honda Technician, I would still find this forum helpful, because there is an art to all this stuff. The art being the correct interpretation of not just OBD and data, but the overt signs and symptoms your vehicle is giving you.
One more technical question if you don't mind. As I have read, the catalytic converter's proper functioning depends on the proper functioning of the upstream O2 sensor(s). In other words, the CC needs the cyclic fluctuations of exhaust gases which result from the rich/lean cycle. These cycles are necessary for the proper chemical reactions to occur in the CC. So the question is, would you replace the upstream O2 sensor(s), ,...downstream,.. along with your CC ? Do you a believe that O2 sensors should be a periodic maintenance item, or are they ?
Again, I'm just trying to understand the Odyssey better,..it's a habit that has served me well with my other cars. If all I wanted to do was to get it fixed, I'd just take it to the shop and be done with it. I'm not opposed to saving some $$ in the process, because a lot of this stuff, I can handle at home,...but mainly I just want to understand the nature of beast.
Thanks
JKP

William Wiles · Dec 20, 2005

I probably not replace the O2 sensors myself with the converter or as a pm issue. The OBD system monitors them and should be able to tell you if they are bad. It monitors the heater circuit, switching voltage and rise/fall time of the sensors. This can also be seen by graphing them on the OBD2 sensor. What happens when the catalyst gets weak is the secondary O2 sensor starts switching closer to the switching rate of the primary O2 sensor. The computer runs tests on this periodically to determine the converter efficiency. On my GM cars the computer outputs this data but Honda does not. However the Ot sensors can be graphed from the continuously running information on the serial bus.
For a lot of good information if you are interested is at http://www.autotap.com/obdii_library.asp and www.howstuffworks.com http://www.obdiicsu.com/Studies/2002CaseStudies/Guidance/Withoutlost.htm ...

I had one other good writeup on P0420 problems but can't find it now. If you want more than you could ever read plug P0420 in Google and loads will come up........

egads · Dec 21, 2005

And all you folks thought you bought cars. They are now computers with an engine.

Ody Fan Club · Jan 13, 2007

I know I'm digging up a thread from a year ago but I wanted to continue the discussion a bit.

I had an intermittent CEL, pulled the codes at Autozone and got a P0401 and P0420. I cleaned out all the gunk in the EGR port with a 17/64ths drill bit, did some other cleaning in the intake/EGR valve and put it back together with a new throttle body & EGR valve gasket. I pulled the battery cable for a few minutes to reset the codes, drove it around a while and went back to Autozone. P0401 is gone but P0420 is back...the weird thing is the CEL never came on.

So...what does the P0420 code with no CEL light indicate? Is there something in between "normal" (no light) and "bad" (light) that the computer stores that indicates "the CAT is going bad but not gone yet"? I have never smelled the rotten egg smell so I would guess it is not the CAT (or is that not necessarily always a positive indicator of a bad CAT?). Or could it be the secondary O2 sensor?

William Wiles · Jan 14, 2007

asingle error does not nesessaraly set a check engine light. Each code is different. The failure is not bad enough to cause the check engine light to come on. It may have been caused by a tempoary flooding of the engine. To help determine if it ia a problem you need to check the readiness code. If it is complete and ready it was probably a temp failure. If it is not ready chances are it will shortly set the check engine light. In other words checking codes without a check engine light can lead to confusion .

Ody Fan Club · Jan 14, 2007

William Wiles said:
To help determine if it ia a problem you need to check the readiness code. If it is complete and ready it was probably a temp failure.

I've never heard of the readiness code...can you enlighten me? I'm assuming that cannot be seen without some ODBII software or through the dealer's diagnostic equipment? I've been looking for something that can display the various sensors, their readings, be capable of possibly adjusting some things, all through a laptop.

William Wiles · Jan 14, 2007

The readiness codes are non-Continuous running tests thare made by the computer. Resetting the codes resets them all to no and it takse several drive cycles to set them. Could take a week in some cases. They have to be looked at with an OBDII testers.

Picture below is from laptop based tester from http://www.obd-2.com/#home

Ody Fan Club · Jan 15, 2007

William...I browsed the obd-2.com site. Alex Peper's credentials and history with OBD is impressive...he's the man! And the software interface looks pretty slick. So for $122, you get the connectors and software that runs on your laptop and is able to access the OBDII info. I have a Honda and a Nissan so all I need is the ISO network and can use it on both cars. Am I missing anything?

How long have you been using the software? Is looks like it is able to store sensor/performance data on your laptop? What shortcomings have you found with the software, if any?

If I got the software, I'd be able to check, among other things, my O2 sensor performance to make sure they were working properly...

William Wiles · Jan 15, 2007

I have used it for about three years or so. It does have some drawbacks but they all do. The consumer scanners Don't have a lot of propriatary information. None of the consumer scanners read the SCS or ABS computer codes or information. You can save scans for future reference or for offline analyzing. So you can set it up in the van and let ir scan the continuously scan items while you drive. I run a scan while driving periodically ans save for future reference and comparison if a problem arises.

You can download the software from his site with a sample scan to check out. It is free. If you do and want an Ody scan to look at let me know by IM and I will send you one.

I have no attachment to Car Code other than using their product. You should look at and compare others packages before you decide on which to buy.

The picture attached is a graph of the VSS and O2 sensers on one of my ODY scans.

Ody Fan Club · Jan 22, 2007

Quick update - after driving the van around for a week, I took it to Autozone Friday to check the codes again. My wife said she had not noticed the CEL on the entire week. Autozone guy plugged in the code reader and voila, no codes found!

I was happy driving around for the rest of the day until the next morning, when I noticed the CEL light on again!!! I was going to go back to Autozone but had a bunch of other errands to run so didn't get a chance to. During my errands, I noticed that the van had been turning over slightly slower than normal so I checked when I had replaced the battery last and sure enough, Jan 9, 2004, almost 3 yrs to the day. My experience is the Honda OEM batteries (and replacement batteries) seem to have a 3 yr timer on them...I have had at least 3 go bad within a few months of their 3 yr anniversary (original battery in the van lasted 3 yrs 2 months).

Since it was a Honda replacement battery, I went back to the dealer to have them load test it and at least recoup 40% of the cost covered on the 5 yr prorated warranty (it was 11 days past the 3 yr full replacement anniversary). The battery failed the load test with only 300 CCA available. My service advisor Neil (same guy that handled my two warranty tranny replacements and politely told me that they couldn't do anything about the EGR TSB due to 116k on the van) said "Well, let me find out what I need to do." Less than 10 minutes later, they had a replacement battery for me and I was on my way with no discussion about the prorate! Incidentally, Honda replacement batteries now have a 100 month warranty for about the same price ($65) as many other 60 month batteries out there...and no modifications required to battery cables/hold down/etc.

This is evidence that it does pay to get to know some of the service and parts guys at the dealer...

rushing1 · Jan 23, 2007

I have the same random P0420 code on my 1999 Odyssey.

I had the Honda EGR TSB performed at 92,000 miles. Even though it was past the 80,000 mile warranty Honda paid 1/2 the repair cost.

The check-engine light came on while I was on vacation with 99,600 miles on the van. I drove 100 miles 1 way to a Honda dealer to have the code checked in case it was set because of the transmission.

The dealer reported the code was P0420 and offered a catalytic converter replacement for $850. I asked if I could safely drive home (1000 miles) to have the repair performed. The dealer said no damage would occur to the van if the performance and mileage remained unchanged. The van was running perfectly, so I decided to return home before having any work done.

One week later, the light went back out. Since then the P0420 code is set occasionally, but within 2-3 tanks of gas it goes back out so I have never replaced the catalytic converter. The light has always been out at emissions inspection time. I now have 157,600 miles on my van.

I have never been able to correlate a gas station / driving pattern that causes the light to come on or go back off. I track the mileage on my van every tankful, and there has been no change. On a yearly basis my van averages 20.6 mpg, +- .3 for combined city (18.5) / highway (23.8) driving. I have gotten as low as 13 mpg in town, and just this Thanksgiving as high as 28 mpg on the highway.

I realize there is no technical data in this post, just a note that another owner has the same random P0420 code.

R2K2 · Jan 24, 2007

I am have the a 99 just like rushing1 with 185,000 miles on it.

The P0420 keeps coming and going. I have replaced the Catalytic Converter and the code still returned.

I then replaced the Downstream O2 sensor and the code still have the same code which keeps returning.

The Upstream sensor was replaced approx. 20,000 miles ago.

I am getting good gas mileage 27 on the HWY and do mostly highway driving. I have tried different GAS stations and as rushing1 said I can not relate it to anything. I am out of options.

Any ideas?

P0420 Code - Oxygen Sensor connection

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