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Discussion Starter · #1 ·
We live in California where the Smog Emissions is the strictest in the country, if not the world! We were notified 6 weeks ago that our Smog Test was due on our 2005 Honda Pilot EX-L and it's been a roller-coaster ride since. First, we had the dreaded PO172 code and ended up having the Valves Adjusted which cleared that issue. Then we had a couple of minor issues that we quickly cleared up. Then, this morning I took our vehicle to our garage to check the codes one more time after driving it for 20 minutes at 55 MPH. Everything looked great until the PO420 code popped up out of nowhere.

I am done spending money on the vehicle but I want to give it one last chance if we can somehow clear this PO420 code without having to replace the Converter. Does anyone have any suggestions? I read that we should check the O2 Sensors. Does anyone have any advice about this?

Thank you!
 

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2016 CRV Touring AWD, 2005 Pilot RIP.
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Cats have a life span of around 150k....so short of replacing the cat with another Honda cat.........or a third gen Pilot.....
 

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Discussion Starter · #3 ·
Cats have a life span of around 150k....so short of replacing the cat with another Honda cat.........or a third gen Pilot.....
Thank you, Rocky! I read somewhere people washing the converter and adding additives to the gas tank to heat up the Catalytic Converter to burn off crap. Have you heard of any reliable process that would possibly allow another 50k out of what I have now?
 

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2016 CRV Touring AWD, 2005 Pilot RIP.
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No I haven't heard of that. The Code in my experience can be persuaded to go away temporarily. Basically, its no longer able to accomplish the cleaning of the exhaust as its catalysts are exhausted.

Either way there is a bullet to bite.....

Sorry, not to be able to send you any good news....
 

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Depending on how long you plan to keep the vehicle you can replace the cat with an aftermarket which may be cheaper than the honda cat. You do need to make sure it's certified for CA.
 

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Nobili spiritus embiggens pequeño sparus tyre.
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There's a debate on whether lacquer thinner can clean your cats.



At this point, as you describe it, what have you got to lose by trying?



There's also something called Cataclean, with which I have no experience. But as mentioned, whaddaya got to lose?

 

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I am in Oregon. I bought a Camry 5 years ago. It seemed like a great car, and I bought it. As I headed out the door, the guy said, the Cat is going out, but we just clear the code and keep going. I couldn't believe it when it lit up in under a week. I cleared it and went a couple months. I now have to clear it about 3 times a year. I have never failed emissions, except one time when I cleared it and went straight to the test. You have to drive about a day before doing that.The check engine light comes on for converters that are working almost all the time but sometimes aren't.
 

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I believe that your 2005 Pilot may have the early 6-3 VCM function. The early VCM has been called out on this forum for causing oil burning after many miles. Some folks have linked the oil burning to catalytic converter problems. You may want to install a VCM disabler (there are several suppliers, I use S-VCM). Reset your trouble codes and take the Pilot for a long freeway drive to heat up the exhaust fully. You might be able to keep the light clear for long enough to pass the smog test.
 

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And there's always the possibility the code isn't accurate. Is the rest of the exhaust sound? Strange leaks in the flex pipe may confuse an oxygen sensor on the downstream end of the cat. Anyway, I have the same issue and am hoping for the best (my flex pipe was just replaced.)

A cheap scan tool that can show live data will reveal if the lower O2 sensor on that side is really reporting erratic behavior. If it's smooth, the code is bunk and will disappear. But if the reading jumps all over the place (like the upstream O2 sensor correctly needs to do) then the cat is bad. I don't believe you can clean precious chemicals that are not sufficiently there.
 

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Nobili spiritus embiggens pequeño sparus tyre.
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I believe that your 2005 Pilot may have the early 6-3 VCM function.
Didn’t that start only in 2006, and only in 2WD models though 2008?
 

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I cleared the code in my sons RAV4 by spraying SEAFOAM directly into the CATs thru the AF Sensors (upstream sensors). Smoked like crazy for a couple hours of driving but cleared the fault.

I should have been more scientific and measured post CAT exhaust pipe operating temperatures to prove the benefit. So I score myself "Plausible"
 

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Don't know if you chose a potential solution yet but our 2007 with VCM and 198k miles threw that code twice in the last six months. First time I used a cat cleaner product and the code cleared for a couple months. After second code popped up I dumped a can of Seafoam in the tank and drove it normally. Code went out after a few days and is clear since.. This vehicle will get traded on something newer later this year so I'm avoiding expenses where possible. Might help your issue. Good luck!
 

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I'm sure everyone knows this already but thought I'd state it here anyway. The 2005 Pilot has 3 cats. Cat's 1 and 2 are on the exhaust manifolds and each has 2 oxygen sensors (an upstream and a downstream). The 3rd cat (furthest from the engine) is after the j pipe and isn't monitored by the computer. I can't say I know what that code is but good luck.
 

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I'm sure everyone knows this already but thought I'd state it here anyway. The 2005 Pilot has 3 cats. Cat's 1 and 2 are on the exhaust manifolds and each has 2 oxygen sensors (an upstream and a downstream). The 3rd cat (furthest from the engine) is after the j pipe and isn't monitored by the computer. I can't say I know what that code is but good luck.
The #3 cat on my 2005 rusted out at the flange few months ago and I replaced it with a straight pipe because both halves of the front flange were gone and it would have been a major repair including the flex pipe. Since that cat is not monitored there are no codes. Two cats are probably enough for cleaning the exhaust. It took some adapters since the inlet and outlet sections are two different sizes. Cost was $10 and a couple hours of work.
 

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Nobili spiritus embiggens pequeño sparus tyre.
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The #3 cat on my 2005 rusted out at the flange few months ago and I replaced it with a straight pipe because both halves of the front flange were gone and it would have been a major repair including the flex pipe. Since that cat is not monitored there are no codes. Two cats are probably enough for cleaning the exhaust. It took some adapters since the inlet and outlet sections are two different sizes. Cost was $10 and a couple hours of work.
Pics?

 

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Had the same issue with our 2007 and tried cat cleaner and seafoam one worked for a few months and the seafoam worked for about a year. After that, we just bit the bullet and put on 3rd party cats we bought from Rockauto and got a few more years out of it before we sold it and got another 2007 with a lot less miles.
 

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Here is what my fix looks like:
How's the sound? My '06 has the original design and it's louder than I'd expect a "family SUV" to be. We got the flex pipe replaced recently and there's zero exhaust noise underneath the front end now. I crawled under the engine and listened while idling and being revved, zero exhaust noise and the rear cat is quiet. But the two rear mufflers give it a bit of a honk. My '06 Accord V6 by comparison is quiet.

Regarding this thread topic, I'm currently monitoring our Pilot's CEL codes. We reliably had a P0420 going into the service for the flex pipe, which I obviously wanted corrected first. Back home and the light is still on, except this time it's both engine cats (P0420 and P0430) AND the code for one of the bottom O2 sensors, the one indicating "slow response."I thought maybe the shop disconnected a lower O2 sensor because of that but the wiring is OK.

Meanwhile, wife takes it out of town and reported the CEL turned off, all codes gone. WTF. I'll find out tomorrow night when she comes back what the latest is.

I'm now looking for a live-stream code reader to see what's actually happening. I know these codes are "popular" with Pilots but this is all new to me. My '06 Accord V6 must be a unicorn, never a CEL unless the gas cap is loose and it's got 226K miles (and a similar overall cat usage from what I understand.)

The irony is that because I live in a rural county there's no safety and no emissions test regardless of year. I could run NHRA headers and straight pipes and I'd be legal. But that fricken' dash light ...
 

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How's the sound? My '06 has the original design and it's louder than I'd expect a "family SUV" to be. We got the flex pipe replaced recently and there's zero exhaust noise underneath the front end now. I crawled under the engine and listened while idling and being revved, zero exhaust noise and the rear cat is quiet. But the two rear mufflers give it a bit of a honk. My '06 Accord V6 by comparison is quiet.

Regarding this thread topic, I'm currently monitoring our Pilot's CEL codes. We reliably had a P0420 going into the service for the flex pipe, which I obviously wanted corrected first. Back home and the light is still on, except this time it's both engine cats (P0420 and P0430) AND the code for one of the bottom O2 sensors, the one indicating "slow response."I thought maybe the shop disconnected a lower O2 sensor because of that but the wiring is OK.

Meanwhile, wife takes it out of town and reported the CEL turned off, all codes gone. WTF. I'll find out tomorrow night when she comes back what the latest is.

I'm now looking for a live-stream code reader to see what's actually happening. I know these codes are "popular" with Pilots but this is all new to me. My '06 Accord V6 must be a unicorn, never a CEL unless the gas cap is loose and it's got 226K miles (and a similar overall cat usage from what I understand.)

The irony is that because I live in a rural county there's no safety and no emissions test regardless of year. I could run NHRA headers and straight pipes and I'd be legal. But that fricken' dash light ...
No change in sound after removing the#3 cat.
 
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