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post #1 of 17 Old 12-12-2013, 05:21 AM Thread Starter
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2007 Accord P0420 AGAIN

Hey Guys,

So last February I had the Check Engine light come on my 2007 2.4 4 cylinder Accord. This code was P0420 and after reading online I thought I would replace the cat and the o2 sensor that plugs into the cat. The car had 65k on it at that point. I reset the code and drove the car for about 10,000-15,000 miles no problems. Now the car is flashing the same exact code less than ONE year after replacing these parts!!


Does anyone have any suggestions as how to proceed? I noticed in our cars we have a mesh flex pipe that is a part of the downpipe prior to the Catalytic converter. Do you think that if this mesh is loose or deteriorating that would cause this code to flash? The last thing I want to do is spend another $200 on a catalytic converter.

FYI I replaced the OEM cat with a MagnaFlow and it is NOT a California car.

Thanks guys!

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post #2 of 17 Old 12-12-2013, 09:50 AM
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Did the same thing on my 99 Civic: replaced the cat with a Magnaflow high-flow cat, then about a year later, got a cell....

Aftermarket catalytic converters are really not as good as OEMs!

What you need now is a O2 sensor spacer to get rid of the cell...or change to an OEM cat.


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post #3 of 17 Old 12-12-2013, 11:39 AM Thread Starter
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I cannot believe the MagnaFlow cat would fail so quickly!! Where can you purchase an OEM cat for under a thousand bucks LOL.

Has anyone tried this O2 sensor spacer with luck?
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post #4 of 17 Old 12-12-2013, 12:14 PM
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Quote:
Originally Posted by NHBP07 View Post
I cannot believe the MagnaFlow cat would fail so quickly!! Where can you purchase an OEM cat for under a thousand bucks LOL.

Has anyone tried this O2 sensor spacer with luck?
Maybe not a lot of Accord guys but tons of Civic Si or other tuner car sites have a wealth of information on this...Basically the spacer gives the O2 sensor false readings by changing its position within the exhaust manifold/pipe. The only thing you want to look for is someone who has run a Dyno w/ Air/Fuel ratio to make sure the spacer doesn't cause the AFR's to go out of whack...some of the Si guys ran into problems with using cheap O2 cheaters...

Mike

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post #5 of 17 Old 12-12-2013, 01:34 PM
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I have done the defouler trick on my factory cat. I use to get the PO420 code every time I drove the car. Then I bought the spark plug defouler from AutoZone for 6 bucks and have not gotten the code since. I will get an PO139 (o2 sensor slow response) about every 4-6 months but that's it.

I also have an 2007 Accord 2.4L
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post #6 of 17 Old 12-12-2013, 01:39 PM
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Never put an O2 sensor spacer on a PRE-cat sensor...In this case, the computer would not be able to know if the air/fuel mixture is correct or not.

No problem to do so on a POST-cat sensor. The only thing it does is to back the sensor from the exhaust flow. Then, the computer thinks the cat does a great job removing some pollutants from the exhaust fumes, and not throwing a cell (in fact, the sensor is just not in the flow of exhaust fumes).


Aftermarket cats will not filter as well as OEM cats. Your Magnaflow had not fail: when new, it would filter as good as OEM, but within a couple months, would not do so anymore. At least, not enough as an OEM, so the computer thinks the cat is bad...

My 99 Civic is like that since 2008, never had a problem...

You can also buy an OEM cat online for less than 1k$. Check on ... You can also buy cheap Denso O2 sensor from rock auto on the web.

**Sorry for my poor English...English is not my primary language

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post #7 of 17 Old 12-12-2013, 01:44 PM
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Quote:
Originally Posted by frenzal View Post
Never put an O2 sensor spacer on a PRE-cat sensor...In this case, the computer would not be able to know if the air/fuel mixture is correct or not.

No problem to do so on a POST-cat sensor. The only thing it does is to back the sensor from the exhaust flow. Then, the computer thinks the cat does a great job removing some pollutants from the exhaust fumes, and not throwing a cell (in fact, the sensor is just not in the flow of exhaust fumes).


Aftermarket cats will not filter as well as OEM cats. Your Magnaflow had not fail: when new, it would filter as good as OEM, but within a couple months, would not do so anymore. At least, not enough as an OEM, so the computer thinks the cat is bad...

My 99 Civic is like that since 2008, never had a problem...

You can also buy an OEM cat online for less than 1k$. Check on ... You can also buy cheap Denso O2 sensor from rock auto on the web.

**Sorry for my poor English...English is not my primary language
: Your English is very good! Nothing to be sorry about. I wish I wrote that well in another language.
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post #8 of 17 Old 12-14-2013, 06:47 AM Thread Starter
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Exhaust downpipe

In our cars, there is a downpipe/header which connects to a flex pip that consists of mesh. This part has a sensor plugged which gets plugged into it. I believe that is the primary 02 sensor (pre cat). The mesh flex portion of this pipe seems to be eroding or...wearing away perhaps. Does anyone know if this mesh flex pipe has an inner pipe that connects? Or; if this pipe was leaking air, could THAT cause a P0420 as air is leaking into the exhaust system and thus causing a bad secondary 02 reading?
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post #9 of 17 Old 12-15-2013, 07:06 AM
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On the V6, there is a pipe underneath the mesh. The mesh is only there for protection... (on my exhaust, the mesh is pretty all gone, waiting for the pipe to be shot before changing that part)

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post #10 of 17 Old 12-15-2013, 09:05 AM
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Quote:
Originally Posted by NHBP07 View Post
In our cars, there is a downpipe/header which connects to a flex pip that consists of mesh. This part has a sensor plugged which gets plugged into it. I believe that is the primary 02 sensor (pre cat). The mesh flex portion of this pipe seems to be eroding or...wearing away perhaps. Does anyone know if this mesh flex pipe has an inner pipe that connects? Or; if this pipe was leaking air, could THAT cause a P0420 as air is leaking into the exhaust system and thus causing a bad secondary 02 reading?
I am pretty sure that mesh can leak on the 4 cylinder. And if it were to leak it could cause that code. The P0420 code can be caused by many different things. I have had this code come and go for a while now and I do suspect I might have a small exhaust leak, or my cat is bad. The winter time is the perfect time to check for a leak. This is what I plan to do soon. Wait til its nice and cold outside, put the front end on ramps or jacks stands and leave the engine running. Then get underneath and inspect for leaks, they should be plainly visible.

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post #11 of 17 Old 12-15-2013, 09:04 PM
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I have a 2006 Honda accord se with 146000 miles. my check engine light came on about 120000 with the p0420. I took it to the dealer cause I looked online and p0420 means bad catalytic conveter. our 7th gen accord 4 cylinder has a pzev engine and our warranty for our emission is 15yrs/150000 miles. take it to the dealer ASAP if your under the warranty they will replace it for free. this warranty will save you $900 + labor for the oem catalytic converter.
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post #12 of 17 Old 12-16-2013, 07:44 AM
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Quote:
Originally Posted by x_treme339 View Post
I have a 2006 Honda accord se with 146000 miles. my check engine light came on about 120000 with the p0420. I took it to the dealer cause I looked online and p0420 means bad catalytic conveter. our 7th gen accord 4 cylinder has a pzev engine and our warranty for our emission is 15yrs/150000 miles. take it to the dealer ASAP if your under the warranty they will replace it for free. this warranty will save you $900 + labor for the oem catalytic converter.
Welcome to Drive Accord...

That FREE work for PZEV vehicles is ONLY if your PZEV car is registered in one of the 8 states that have "California" emissions. I have a PZEV vehicle, but my car is registered in Illinois, so my catalytic converter is NOT covered.

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post #13 of 17 Old 12-16-2013, 03:07 PM
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Quote:
Originally Posted by NHBP07 View Post
I cannot believe the MagnaFlow cat would fail so quickly!! Where can you purchase an OEM cat for under a thousand bucks LOL.

Has anyone tried this O2 sensor spacer with luck?
Cintocrunch is right, these are very popular for the Civic owners who eliminate their stock cat with race headers. We have a very good one which is angled so you don't have to worry about the O2 sensor being broken if it's a tight fit with the body.
Check it out here:
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post #14 of 17 Old 12-16-2013, 03:41 PM
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Quote:
Originally Posted by x_treme339 View Post
I have a 2006 Honda accord se with 146000 miles. my check engine light came on about 120000 with the p0420. I took it to the dealer cause I looked online and p0420 means bad catalytic conveter. our 7th gen accord 4 cylinder has a pzev engine and our warranty for our emission is 15yrs/150000 miles. take it to the dealer ASAP if your under the warranty they will replace it for free. this warranty will save you $900 + labor for the oem catalytic converter.
P0420 does NOT necessarily mean your cat it bad. It can also be a bad O2 sensor, bad air/fuel ratio sensor, bad sensor wiring, or an exhaust leak before the cat. All of that should be checked first.

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post #15 of 17 Old 12-18-2013, 06:47 PM
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Originally Posted by Straight Drive View Post
P0420 does NOT necessarily mean your cat it bad. It can also be a bad O2 sensor, bad air/fuel ratio sensor, bad sensor wiring, or an exhaust leak before the cat. All of that should be checked first.
That is correct, the P0420 code is just a symptom.

Possible PO420 code causes

The following engine related problems are known to generate the PO420 code:

Intake manifold air leaks
Fuel injector problems (leaks)
Incorrect spark plugs
Ignition timing
EGR problem
Defective catalytic converter
Oil or antifreeze entering exhaust
O2 sensor not operating correctly
Road damage to converter
Silicone contamination


Silicone-based products or Teflon sealants should not be used on any part of the exhaust system. They are not designed to operate at high exhaust temperatures and will out gas, causing damage to O2 sensors.



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