I'm OK with replacing it. my time is cheap and the cost difference in a HONDA cat is significant. I paid $188 for the B1 Cat, AP Eastern brand...vs $1150 for OEM Honda at Bernardiparts.com

I mean we're talking about a nearly 20 year old vehicle here, in South TEXAS where there are no emissions testing and most everyone drives huge trucks, diesels, or like maniacs.

I drive round trip less than 20 miles per day. I will take your 6 month bet, say for $500?

 

As long as you know going in. Many people expect them to fit and work like the factory one. There's a reason one is $188 and the other is $1150.

 

Thank you all for your knowledge and willingness to share on this thread.

I have replaced all 4 O2 sensors to treat a p0420 CEL.
As mentioned earlier, the hardest part is the dang clips...especially Bank 1.

I cleared the codes and have monitored via OBDwiz.

I get a lot of fluctuation on Bank 1, looks like I will need to replace that cat. Using a cheap cat from RockAuto, I'll report back if there are issues.

 

... Using a cheap cat from RockAuto, I'll report back if there are issues.

There's about a 95% chance that will not go well and you'll be doing the job again. Even if it does work at first I would bet money it will fail in 6 months.

 

Thx.

It does seem to me that the B1 V and alpha numbers are still bouncing around more than for B2, but it's hard to keep a close eye on them while driving (and when I coast, ECO mode kicks in and mostly shuts off the engine anyways).

The car was smogged in Jan, and CA is every two years. I only need to smog it because it's required for a private sale of a used car to be smogged within the last 90 days. So far haven't had (made) time to go smog it, and then slam that CL up there and hope for the best!

 

Good to hear. Remember, your P0420 may still come back. The cat could be just on the edge and pass sometimes and fail sometimes. I'd get it smogged right away before it comes back. If it comes back then you have a year to get the cat replaced. The good thing is that if you need to replace the cat then you'd want to replace the O2's anyway. Besides, new O2's make the engine run like new...at least that was my experience.

 

Long story short, I went and stuck my hand back behind bank 1 and tried to unclip the bracket. No way. Not after remembering the couple hours of hell I went through with bank 2 sensor 1 last year, and that's when I could see it!

I called a local muffler shop with good yelp reviews, he said $45/labor per sensor, plus parts if he needed me to order them. (So obviously no objection to online ordering!) I ordered NTK sensors from rockauto, brought them to the guy, got the van back, and not only did he replace the sensors, and there's no trouble or pending codes showing, he also ran the car through enough cycles to set the readiness codes! Big shout out to WTB muffler in Poway, CA.

Next step get it smogged, then put it back up on craigslist.

Thanks all, esp. John Clark for patient, detailed description of what's up. You guys rock!

 

For reference, this (long!) video seems to be very exhaustive on how to replace sensors on a Gen3, even with special tips about where to position yourself, how to insert one or both arms/hands, etc.

 

Check the prices at the Honda dealer for the same O2's and you'll see that RockAuto is a real bargain. Considering that the O2 sensor lives in a very harsh environment, and is the heart of the fuel control for the engine, replacing them by 150K is not a huge investment. I replaced mine at 170K and I wish I'd have replaced them closer to 150K.

 

Great detailed info John. I have the same tool pictured but like Max have also cut the wires on stubborn sensors. Way more confidence when you have a fat 1/2" drive socket & ratchet on their.

At Rockauto it looks like there are 3 NTK sensor part numbers. Maybe because of cable lengths? Looks like about $140 plus shipping. This search is for the year of my van, 07. Looking at 05 I see 24302 for $116 each on the bottom one and you'd need two. Ouch.

24259 - Downstream Front; OE MFR: NTK $55
24255 - Downstream Rear; OE MFR: NTK $55
24346 - Fits Upstream Rear; OE MFR: NTK Or Upstream Front; OE MFR: NTK $64 (for 07, 05 looks to be 24302 for $116ea)

Direct link to Rockauto 05 Odyssey.
2005 HONDA ODYSSEY 3.5L V6 Oxygen (O2) Sensor | RockAuto

 

I've had pretty good luck with this style O2 sensor tool:

The above hasn't yet failed me. I also have the slotted deep well style socket and it doesn't seem to work as well. I've noticed it likes to flex too much. Cutting the wires and using a box wrench is also a good method but once you do that you're definitely committed.

 

I've had pretty good luck with this style O2 sensor tool:.

Is that a universal size for any O2 sensor? When I changed the one, O'Reilly's offered me a loan of one of those, but maybe I should just buy one.

EDIT: looks like it...

 

Thanks, this is all very helpful.

I don't remember what kind of sensor I put in, I'm pretty sure it was a cheaper one, not an OEM one. Bosch maybe. If I call O'Reilly I think they can look up my purchase history from my phone number and tell me. I guess this is an opportunity to buy myself a crow's-foot as well.

If I end up having to replace the bank 1 cat, since OEM seems to be the only reasonable option, I guess I'd have to get that from the dealer.

 

There are special tools for removing oxygen sensors, so I suggest you look into that, but personally I have found that box wrench (closed loop) works best for taking off
old stuck sensors. Especially if you are replacing it, you can just cut off the pig tail. Alternatively, deep socket also works but depending on the location.

There are a ton of online honda dealers that sell parts at 25-30% off msrp. The trick is of course to buy online, vs going to physical parts dept at the local dealer.
I like BernardiParts.com on east coast but have bought from many different ones. Yes only buy OE Honda catalytic converter. Not only will it provide perfect fit,
it should last as long as original one did, provided, as John mentioned, you get at the root problem that caused it to fail, so definitely good recommendation to replace
both pre and post o2 sensors.

 

The O2 that is on top and up front is B2S1. So, that B2S1 O2 failed and you replaced it--Got it. Now you have a P0420 code which is for Bank 1, not Bank 2. So, the cat that is failing is actually on the rear bank and is not associated with the original failed O2 sensor that is on bank 2 (front bank.) Cats don't usually fail for no reason...there's usually a cause and that cause is usually too much fuel/too rich a mixture going through it.

I stand by my original recommendation. I don't know what kind of O2 sensor you replaced the failed one with but you want to use ONLY and NTK or Denso sensor, and preferably an NTK since that's what Honda used as the original sensor. I would replace all four sensors with new NTK sensors from RockAuto. If the one you already replaced is an NTK or Denso then don't replace that one but definitely replace the other three with NTK's. If you replaced the failed sensor with a Bosch or other brand sensor, or universal sensor, then I'd replace it again too. Then clear the codes and drive it for a while and see if the P0420 comes back. If it does, then replace the rear bank (bank 1) cat.

 

Thanks for the tutorial. 'forward' is just what I thought I remembered the guy telling me. Also 'upstream'. Engine light came on while in CO on a road trip, a guy in a shop scanned it for me and told me I could deal with it after I got home. (Complicating things, my battery also died. O'Reilly's in Santa Fe NM really came through and gave me a total replacement (not even prorated) just because I was out on the road.)

The sensor I replaced is in the front of the car (I guess bank 2), on 'top'. You have to reach down between the engine and the radiator. Is that upstream, B2S1? Is the other sensor for that cat on its bottom end, reachable from underneath?

It makes sense to replace the sensors first and see if that does the trick. You've inspired me to to at least crack the hood see if I can get an eyeball on all 4 and evaluate whether I'll be able to reach them.

 

First you have to start referring to the O2 sensors in a way that we can understand which one(s) you're referring to. There is no "forward" O2 sensor. When you say "forward" are you referring to "forward" as being on the front of the engine or forward of the cat? If forward of the cat, which cat, i.e. on which bank?

There are FOUR sensors on the gen 3 Ody. There are two on each bank. There is an upstream and a downstream with reference to that bank's cat. So, there is bank 1 sensor 1 (B1S1) and sensor 2 (B1S2,) and then there is bank 2 sensor 1 (B2S1) and sensor 2 (B2S2.) So, when you say "forward" I have no idea which O2 sensor you're referring to.

The upstream sensors (B1S1 and B2S1) job is to measure the oxygen content in the exhaust and send that information to the PCM. The PCM reads that information and changes pulse width of the fuel injector ON time. If the sensor is reading that the mixture is lean then the PCM will turn on the injector for a longer duration, thus enriching the mixture. If the sensor reads that the mixture is rich then the PCM will reduce the injector ON time, thus leaning out the mixture.

The downstream sensor, in most vehicles, is just used for comparing the oxygen content in the exhaust downstream of the cat with that of the oxygen content upstream of the cat. This comparison is how the PCM knows whether the cat is doing its job.

What complicates things with this generation of Honda is that the upstream sensors are actually Air/Fuel Ratio sensors, or wideband O2 sensors. These sensors work differently than standard O2 sensors and are more difficult to diagnose. Additionally, Honda, when using A/F ratio sensors, uses the downstream sensors in its fuel control strategy which complicates things even more.

P0420 and P0430 occur when the computer sees similar data from the downstream sensor compared to the upstream sensor. If the downstream O2 sensor data (measured in millivolts) stays fairly steady then that usually indicates a working cat. If it is fluctuating between 50mV and 900mV fairly rapidly then that usually indicates a failing cat. The idea is that the exhaust leaving the cat should be different than the exhaust entering the cat. If it's the same then it's not doing its job and you get P0420 (or P0430 on bank 2.)

If it were me, I'd replace all four O2's with new NTK sensors from RockAuto and drive it for a while and see what happens. If the P0420 or P0430 returns then I'd replace the appropriate cat. At 170K it needs all four sensors replaced anyway as they're worn out and contaminated after so many miles. If the P0420 returns then you need a new cat and want new sensors with a new cat regardless.

 

If the downstream O2 sensor data (measured in millivolts) stays fairly steady then that usually indicates a working cat. If it is fluctuating between 50mV and 900mV fairly rapidly then that usually indicates a failing cat.

I found a screen on my ultragauge showing data for all 4 sensors. The downstream numbers were almost always close to 1, the upstream numbers were normally around 0.800. One was called "V" one was called lambda, I don't remember which was which. When coasting (and ECO comes on and presumably the fuel cut-off is activated), those numbers changed to 2 and 0, which made things confusing. But I think I detected times where, under fairly steady gas pedal, the 0.800 number would dip to 0.100 or less for a little bit. I guess that's what you're talking about.

 

I replaced the forward O2 sensor when I got a code for that. I never got a code for the O2 sensor on the other cat, and I don't know anything about any other two O2 sensors.

I have an ultragauge scanner, what should I look at to read/interpret live O2 data? What numbers should I expect to see?

 

P0420 is the rear bank (bank 1 as explained already is where the #1 cylinder is.) The P0420 code almost definitely indicates a bad converter, however, the only real way to know for sure is to look at the O2 sensor live data on a scan tool. Replacing the cat will solve the P0420 code. The one thing to keep in mind is why the cat failed to begin with and preventing future failure of the new cat. Did you drive for a long period of time with an O2 sensor code indicating a failed O2 sensor? If so, that might be what damaged the cat. If it were me and I was replacing a cat I would make sure ALL FOUR oxygen sensors were replaced at the same time with the OEM replacements. OEM sensors are NTK and can be purchased pretty inexpensively on RockAuto.com.

I just replaced all four of my O2 sensors at 170K as they were pretty worn out as indicated by the fuel trims in the live data on my scan tool. I got a 10-20% increase in fuel economy when I was done. I won't go into how the Honda uses all four sensors for fuel strategy but it's definitely worth it to replace all four sensors.

 

Found this video for a 2003 Accord V6 VTEC, with 3 cats, engine looks similar, position of cats looks similar, is this a good description of the process to replace rear cat in the Odyssey?

Seems wicked hard (for me), tons of bolts that are hard to reach/get leverage on.

But it looks like this guy had just P0420, and replaced only the one cat. Hopefully I can get away with that too.

 

I have never done a rear cat on ody, but I imagine that it will be relatively hard job to do. The rear bank access will be mostly blind, reaching over the entire engine to undo 4 nuts that hold the top of the cat to exhaust manifold. The bottom 3 bolts or nuts are not too bad, as long as you got an impact tool and the fasteners are relatively rust free.
But one broken stud will make your life miserable. You wont know until you try.
If possible, just disconnect the o2 sensor harness and leave them in, it will be much easier to remove the sensors on the bench.
Likewise, install the o2 sensors before installing replacement cat. Use new gaskets.

 

The rear bank access will be mostly blind, reaching over the entire engine to undo 4 nuts that hold the top of the cat to exhaust manifold.

That's what I was thinking; when I replaced the forward O2 sensor it was hard enough to get at when I could see it, and I could barely reach&feel the rear one, I was thinking no way I could do this blind! But maybe there's a way to prop myself up on top of the engine so I can see behind there?

The bottom 3 bolts or nuts are not too bad, as long as you got an impact tool and the fasteners are relatively rust free.

So I asked a buddy if he could maybe help me with the cats, he's a lot more experienced than I am with auto repair -- but he said as far as he knew cats always had to be welded on/off. Is he just used to older cars? Gen2 looks like just bolts, and it sounds like Gen3 as well.

 

Yes it is VERY easy to remove and install no complicated or special tools needed. Just remove 3 bolts from the front and back of the converter and install the same way. If your bolts and nuts looks corroded then you may have to have the shop to heat it up and make a hole to put new one in if you broke one. I heated mine with propane until it becomes glowing cherry red then quickly unscrew it nice and slow.

 

Are you sure you're talking about the same model? When you say 'front and back', it sounds like a single large cat that is underneath everything, like I've seen a video on utub about the gen 2 odysseys. This is gen 3, with 3 smaller cats, two of which run vertically at the front and back of the engine. I can't find a video of how to remove those, but another post a guy was talking about how the rear one could barely fit out a complicated path through the passenger wheel well.

Fortunately though, this ody has lived its whole life garaged in San Diego, so I think best possible chance bolts would not be corroded/rusted. Just how hard are they to get to?

 

Yes, there are three cats on the gen 3. The TWO forward ones are monitored. P0420 is for bank 1 (rear bank) and P0430 is bank 2 (front bank.) If you struggled with the O2 sensors then the cat won't be any easier. I replaced all four O2's on my 08 Ody and it wasn't that bad. Hardest thing was the wire harness clips. For the cat you'll have to remove the flex pipe section of the exhaust and then the four bolts that hold the cat to the cylinder head.

 

P0420 is for bank 1 (rear bank) and P0430 is bank 2 (front bank.)

Are you sure that's right? It would make more sense to me if bank 1 is front and bank 2 is rear. Isn't that the order of flow, front to rear (1 to 2)?