Surviving the dreaded P0420 Code (Cat Converter) 1st Gen There Is Hope!

1044 Views 7 Replies 6 Participants Last post by Jtxl, 11 h ago

RVoegtly

Discussion Starter · 10 mo ago

My 2008 EX-L started throwing a CEL with a P0420 fault code about a year ago at 215,000 miles. Currently at 235k miles, all original parts in the exhaust/emissions system. Cleared the code with my Actron reader and it came back sporadically about 4 times. Each time it cleared and stayed off for a couple/few months, no performance or gas mileage issues noted. Then the dreaded “California SMOG check required” shows up in the mail.

In May, I got with my local independent mechanic who tells me 100% of the time its the Bank 1 Catalytic Converter and that it will fail SMOG with that fault. (Note - he also does SMOG tests) That checks with everything I’ve read in this forum, so we agree that he’ll order the CARB compliant one from Honda and will let me know when it’s in. Estimate for the whole job is $1,800. ($1,400 parts). The back order pushes two times and in late July he tells me it will now be September at best before they’ll have parts on hand. My registration expires 31 July…

So I got a second opinion from another equally trusted mechanic (who does NOT do SMOG testing). He reports that if I can get the Fault to clear and all monitors to set to ready, it should pass smog. That was easy enough to do, but comes with the risk that something trips on the way to the SMOG station leading to a failed test and me parking the car until I can throw $1,800 at a mechanic to throw an new Cat in it. Risk taken (with a quick code scan a block from the test station), Test passed, and 2 more years of owning and operating this amazingly reliable vehicle in Southern California enabled.

Lessons learned: 1. A mechanic who also does SMOG testing will probably not give advice which undermines the ‘sanctity‘ of the SMOG test process. 2. Don’t wait to get a second opinion on any job over $500.

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killster2smallbox

· #2 · 10 mo ago

RVoegtly said:
My 2008 EX-L started throwing a CEL with a P0420 fault code about a year ago at 215,000 miles. Currently at 235k miles, all original parts in the exhaust/emissions system. Cleared the code with my Actron reader and it came back sporadically about 4 times. Each time it cleared and stayed off for a couple/few months, no performance or gas mileage issues noted. Then the dreaded “California SMOG check required” shows up in the mail.

In May, I got with my local independent mechanic who tells me 100% of the time its the Bank 1 Catalytic Converter and that it will fail SMOG with that fault. (Note - he also does SMOG tests) That checks with everything I’ve read in this forum, so we agree that he’ll order the CARB compliant one from Honda and will let me know when it’s in. Estimate for the whole job is $1,800. ($1,400 parts). The back order pushes two times and in late July he tells me it will now be September at best before they’ll have parts on hand. My registration expires 31 July…

So I got a second opinion from another equally trusted mechanic (who does NOT do SMOG testing). He reports that if I can get the Fault to clear and all monitors to set to ready, it should pass smog. That was easy enough to do, but comes with the risk that something trips on the way to the SMOG station leading to a failed test and me parking the car until I can throw $1,800 at a mechanic to throw an new Cat in it. Risk taken (with a quick code scan a block from the test station), Test passed, and 2 more years of owning and operating this amazingly reliable vehicle in Southern California enabled.

Lessons learned: 1. A mechanic who also does SMOG testing will probably not give advice which undermines the ‘sanctity‘ of the SMOG test process. 2. Don’t wait to get a second opinion on any job over $500.

well im in cali and had the exact same issue, not sure if you have read the forums at all but i got mine to clear by installing a defouler on bank 1 sensor 2 (took 2 seconds to install) i then ran premium gas 4 tanks though the car and cleared teh code witha odbII reader. it has clearned the issue and passed smog just fine. i did also order a non carb compliant bank 1 cat for 120 on ebay but never had to install it. (i did also change the spark plugs but doubt it did much)
now if you go to the smog place adn teh check engine light goes on of course you dont try to smog and come back when t is off. i drove with expired tags since may till i got around to installing the defouler (15$?)

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RVoegtly

Discussion Starter · #3 · 8 mo ago

A long overdue thanks for that reply and references. Did you notice any performance or fuel mileage improvement after installing the defouler + 4 tanks of premium?

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Nail Grease

· #4 · 8 mo ago

If that 2008 is a 2wd, I’d disable the VCM. Doing so ended my emission codes permanently. Disregard if 4WD.

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smallboxkillster1

· #5 · 8 mo ago

RVoegtly said:
A long overdue thanks for that reply and references. Did you notice any performance or fuel mileage improvement after installing the defouler + 4 tanks of premium?

I installed the svcm 1000 miles after passing smog, I don't think using premium or a defouler would give you better gas mileage. The svcm has taken 2mpg from me but hopefully that lost milage will even out in future repairs it may or may not help. I'll keep you posted. And I still have a extra new bank 1 cat when ever it fails. (Was only 120 compared to a cali carb version for 1200)

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Nail Grease

· #6 · 8 mo ago

Id replace the EGR valve.
Id also do a throttle body cleaning with a throttle reset.
I assume you have a new/clean air filter, installed correctly, box lid sealed. Intake hose is leak/crack free.
I agree, premium gas does little. I’d look for 87 octane with fuel additives (top tier).

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the ed dude

· #7 · 2 mo ago

Thanks for the tips above.

I'm dealing with this code issue now as my inspection is due and need the CEL to go away. 2007 Pilot with 213k miles. I've cleared it and it comes right back after the emission test cycle completes. I took a look at some live data on the OBD scanner to see if it could be a sensor issue, but I'm not really sure how to translate it. It seems like the sensors work normally. Here is some screenshots comparing both bank's downstream sensors.

Font Screenshot Technology Circle Rectangle

Font Screenshot Technology Terrestrial plant Circle

It would be nice to not have to change out the cat so the defouler thing is interesting. Right now I'm going to reset the code and add some seafoam to the gas tank and do the intake cleaning. I'll also take a look at EGR. I've recently done a throttle body cleaning, replaced knock sensor, and suspension work but the code was around prior.

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Jtxl

· #8 · 11 h ago

My code went away with duralube extreme catalytic converter cleaner. I hear an extra washer on the o2 sensor on the cat will keep it backed off enough to not throw bad codes. If I ever get mine off I will try it.

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