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Old 04-28-2009, 06:55 AM   #1
Atomic1
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Default P0420 code question

B16 here

Can a leak at the joint between the A pipe and catalytic converter cause a P0420 code "Cat efficiency"?


My primary O2 sensor is mounted on the A pipe, and the secondary on the cat converter bung.
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Old 04-28-2009, 08:53 AM   #2
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Default Re: P0420 code question

i believe its ur converter that is bad
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Old 04-28-2009, 10:15 AM   #3
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Default Re: P0420 code question

could be a bad cat depends where the primary o2 was installed. how far in front of the cat ?
and if its on the flange area then most likely a bad cat.
the leak between the a pipe and the cat could cause a issue but depends on the leak how bad is the leak?
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Old 04-28-2009, 04:32 PM   #4
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Default Re: P0420 code question

Stock setup. The primary O2 sensor is mounted on the stock A pipe.....so about 6" from the joint. The secondary sensor is on the outlet end of the stock cat.

Can a leak between the primary O2 sensor and the cat cause a catalyst inefficiency problem?


I understand that this code means my secondary sensor output isn't flat enough, but what I'm asking is if a leak where I described will cause the catalyst to underperform.
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Old 04-28-2009, 09:14 PM   #5
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Default Re: P0420 code question

could cause a exhaust dilution during a smog test but it would have to be open to create a condition like that.
most likely a bad cat.
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Old 04-29-2009, 05:57 AM   #6
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Default Re: P0420 code question

Interesting, I have another Master Honda Tech telling me this:

Running rich will decrease catalyst efficiency.
Running lean will decrease catalyst efficiency.
Exhaust leak before the cat will decrease catalyst efficiency.


I'll have to find out why....
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Old 04-29-2009, 07:07 AM   #7
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Default Re: P0420 code question

po420 code sets when switching time between front and rear 02's is out of range...it does not automatically mean the cat is bad

an overly rich condition will cause the code because of the excess fuel in the exhaust stream causing the rear 02 to "think" the cat is bad because it did not see enough of a change from the front 02 reading

an overly lean condition will cause the code for the same reasons

also both of these conditions can cause the catalyst to operate outside of it's intended temperature range...the same thing that an exhaust leak ahead of the rear 02 will cause to happen

I've seen people throw cats in a car for a po420 code that really only needed a tune up...brand new cat installed, cel cleared, and a week later the code is back on the the po420 and throwing a new set of plugs in it keeps the light out...

so...check your tune up stuff, and fix your exhaust leak and your po420 code will probably go away...hope that helps
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Old 04-29-2009, 10:21 AM   #8
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Default Re: P0420 code question

Quote:
Originally Posted by 92_civic View Post
I've seen people throw cats in a car for a po420 code that really only needed a tune up...brand new cat installed, cel cleared, and a week later the code is back on the the po420 and throwing a new set of plugs in it keeps the light out...
Exactly why I'm asking before following the knee jerk reaction everyone seems to have with the P0420 and replacing the $800 stock cat.

Will try to narrow the problem down. thanks
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Old 04-29-2009, 10:25 AM   #9
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Default Re: P0420 code question

let us know what you find then.
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Old 04-29-2009, 10:28 AM   #10
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Default Re: P0420 code question

here is some more food for thought


Before Checking a Catalytic
Converter DTC
Before you troubleshoot an OBD II vehicle that stores
DTC P0420 (67) (catalyst system efficiency below
threshold), run these quick checks:
1. Check for a leak in the exhaust system. If you find
one, repair it, clear the DTC, and test-drive the
vehicle.
• If the DTC doesn’t come back, return the vehicle
to the customer.
• If the DTC returns, go to step 2.
2. Connect the PGM Tester, and test-drive the vehicle
while an assistant monitors the voltage signal from
the secondary oxygen sensor (HO2S S2). After the
catalyst reaches operating temperature, the HO2S S2
voltage should stay between 0.5 and 0.8 V at steady
cruising speed. During deceleration, the voltage
should be steady at 0.1 V or less.
• If the voltage readings are OK, clear the DTC, and
return the vehicle to the customer.
• At cruising speed, if the voltage fluctuates or stays
below 5 V, go to step 3.
3. Measure the inlet and outlet external temperatures of
the catalytic converter with a thermometer capable
of reading up to 500F.
• If the outlet temperature is more than 100F hotter
than the inlet temperature, the converter is OK;
clear the DTC, and return the vehicle to the
customer.
• If the outlet temperature is less than 100F hotter
than the inlet temperature, replace the converter.
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Old 04-29-2009, 12:10 PM   #11
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Default Re: P0420 code question

^^^^^

bingo! the temp test and 02 voltages test was the part I left out on my first post, I was just coming back to add to it, but you beat me to dtapia
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Old 04-29-2009, 12:36 PM   #12
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Default Re: P0420 code question

So what are the results
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Old 04-29-2009, 12:56 PM   #13
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Default Re: P0420 code question

I wont be able to get under the car until next week. Once I get back to my normal garage I'll fix the gasket leak and let you guys know the results.

Last edited by Atomic1; 04-29-2009 at 01:07 PM.
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Old 04-29-2009, 07:51 PM   #14
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Default Re: P0420 code question

we will be here.
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Old 04-30-2009, 07:08 PM   #15
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Default Re: P0420 code question

I am very interested in the results bumpdy bump
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Old 04-30-2009, 07:17 PM   #16
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Default Re: P0420 code question

if the cat is bad you can always add in a o2 extender on the secondary o2, and then you wont need a cat $5 fix
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Old 04-04-2010, 01:08 PM   #17
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Default Re: P0420 code question

.

Last edited by Atomic1; 04-04-2010 at 08:37 PM.
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Old 04-04-2010, 04:06 PM   #18
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Default Re: P0420 code question

Quote:
Originally Posted by Atomic1 View Post
B16 here

Can a leak at the joint between the A pipe and catalytic converter cause a P0420 code "Cat efficiency"?


My primary O2 sensor is mounted on the A pipe, and the secondary on the cat converter bung.
Yes, it could.
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