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Old 01-11-2005, 01:48 PM   #1
C2H5OH
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Default Honda question - 420 CEL (Cat Inefficiency)

Hey guys,
My gf's accord is throwing a CEL - Autozone's reader's scanned it at 0420... some blah..blah... cat being inefficient. Do you think I could use some kind of MIL eliminator to get rid of the code or if there anything else that I could do?

Appreciate any input on the issue
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Old 01-11-2005, 01:53 PM   #2
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Well depending on the actual code (high/low, no response) it could be the sensor as well as or in addition to the cat....

if its the sensor I dont think the MIL eliminator would work but if its the cat than yeah it would get rid of the light but you still wouldnt pass emissions with a sniffer
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Old 01-11-2005, 02:08 PM   #3
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my Honda throws MILF codes all the time boi! especially at the female Z06 drivers
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Old 01-11-2005, 02:58 PM   #4
C2H5OH
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Quote:
Originally Posted by WRX300
Well depending on the actual code (high/low, no response) it could be the sensor as well as or in addition to the cat....

if its the sensor I dont think the MIL eliminator would work but if its the cat than yeah it would get rid of the light but you still wouldnt pass emissions with a sniffer
Thanx - the actual code was something like cat running below or with low efficiency, so I doesnt sound like a bad sensor. On the other hand, she just smogged that accord! Just caught one of the days when CEL was off and it passed the test. I'm puzzled...
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Old 01-11-2005, 02:59 PM   #5
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Code 0420 means you need to stop fishbowling in yuor Honduh.
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Old 01-11-2005, 03:00 PM   #6
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CHeck your gas cap.
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Old 01-11-2005, 03:03 PM   #7
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Quote:
Originally Posted by C2H5OH
Thanx - the actual code was something like cat running below or with low efficiency, so I doesnt sound like a bad sensor. On the other hand, she just smogged that accord! Just caught one of the days when CEL was off and it passed the test. I'm puzzled...


would probably be the o2 sensor itself then... especially if it passed a sniffer
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Old 01-11-2005, 03:06 PM   #8
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Quote:
Originally Posted by soso3
CHeck your gas cap.
Check it for what? If it's closed? For leaks? The car's been recently smogged and I'm sure they checked it...
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Old 01-11-2005, 03:08 PM   #9
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Quote:
Originally Posted by C2H5OH
Check it for what? If it's closed? For leaks? The car's been recently smogged and I'm sure they checked it...
gascap will throw a CEL for "small evap systems leak detected" not a cat ineffiency code
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Old 01-11-2005, 03:14 PM   #10
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Old 01-11-2005, 03:14 PM   #11
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p0420 happened on my GF's old 2002 accord, and JUST happened on my coworkers 98 accord. Dealership said that they need to replace the catalytic converter for that code. Keep in mind it (the cat) is covered until 80,000 miles on a honda.
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Old 01-11-2005, 03:19 PM   #12
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Quote:
Originally Posted by WRXVT
p0420 happened on my GF's old 2002 accord, and JUST happened on my coworkers 98 accord. Dealership said that they need to replace the catalytic converter for that code. Keep in mind it (the cat) is covered until 80,000 miles on a honda.

the 8/80 is federal warranty from all OEM cars

EDIT: most OEMS will do the CAT itself under this warranty but if your o2 sensor(s) crap out you gotta pay for it yourself

Last edited by WRX300; 01-11-2005 at 03:30 PM.
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Old 01-11-2005, 03:31 PM   #13
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Yup federal law
8 years 80k on the Catalytic Converters and PCM.

A bad 02 sensor will not cause a p0420, if its under 8 years 80k take it to the dealer and have them look at it.

Jay
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Old 01-11-2005, 03:40 PM   #14
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What year of accord?

My friends Si was throwing a similar code (cat inefficiency) and he just put an 02 sim on it (then again, he's now running a race header which eliminates the cat) and that worked.
Another friend had a bad 02 sensor, Honda replaced it.
My car got a CEL the other day - I never checked it, actually - but I reset the ECU and it didn't come back on. Might want to try that first, if it comes back up get Honda to peek at it.
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Old 01-11-2005, 07:39 PM   #15
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Thanks for the information I think it's a 97 accord, and it's over the 100,000 by now, so it's out of warranty... But, it has passed a smog check within a couple of months for sure. As wrx300 pointed out, it's more likely to be an O2 sensor than a cat since it passed a sniffer test without issues.

So far, I'm going to (1) reset an ECU, (2) if the CEL comes back, search for an electrical CEL fix (if it worked on a WRX, it should be fine for an Accord - and there is NO way i'm gonna spend time trying to custom fit a mechanical one), (3) take a look at a gas cap, just in case, and check whatever else is related to emissions and is easily reachable.

Why wouldnt a bad sensor cause a p0420? I was under impression that if reads incorrectly, it will be sending wrong voltage back to the ECU... Is 420 associated with cat converter itself or can it be caused also by something else, for example, a bad air/fuel mixture?

Again, thanks for all the input!
-Alex
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Old 01-11-2005, 07:43 PM   #16
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My Legacy will throw a P0420 code once or twice a year. I'm guessing that the oxygen sensors need replaced rather than the actual cats. I just can't justify spending the $180 on an old car when it is running strong as ever at 135k miles.
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Old 01-11-2005, 07:47 PM   #17
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Quote:
Originally Posted by BJamerican
My Legacy will throw a P0420 code once or twice a year. I'm guessing that the oxygen sensors need replaced rather than the actual cats. I just can't justify spending the $180 on an old car when it is running strong as ever at 135k miles.
I think it's more like $50-70, but still... I know what you mean
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Old 01-11-2005, 07:48 PM   #18
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Quote:
Originally Posted by McDade
Yup federal law
8 years 80k on the Catalytic Converters and PCM.

A bad 02 sensor will not cause a p0420, if its under 8 years 80k take it to the dealer and have them look at it.

Jay
But doesn't the ECU use the O2 sensors to determine cat efficiency by comparing their readings? Couldn't it throw a P0420 if one of the sensors is fouled as long as the reading isn't deemed invalid by the ECU?
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Old 01-11-2005, 07:49 PM   #19
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Quote:
Originally Posted by C2H5OH
I think it's more like $50-70, but still... I know what you mean
But there are 2 oxygen sensors to replace.
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