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P0420 Code

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Old 01-20-2012, 09:16 AM   #1
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Icon2 P0420 Code

I have a 2007 4 cylinder accord with 89,000 miles on it. The check engine light came on this week and I checked the code which was P0420 (Catalyitc Converter). Am I going to need to replace the sensor, or the Cat itself? Also, I am supposed to be driving about 250 miles on Sunday, does this need to be fixed before I make that trip? Thanks.
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Old 01-20-2012, 09:34 AM   #2
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Default Re: P0420 Code

The p0420 is the cat converter. Yes you will have to replace the whole cat not the o2 sensor. Yes it will be ok to drive on your trip with no problems. Just need to take it to a dealership and have a factory converter installed. Aftermarket will work but the light will come back on eventually.
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Old 01-20-2012, 09:39 AM   #3
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Default Re: P0420 Code

It usually is the cat....sometimes the sensors both follow right after....you should be fine for the trip. On my civic I use for an every day driver, I installed a high flow cat...which is less expensive by the way....to get the down stream sensor to read right, you should installed a spark plug non fouler drilled out about a half inch and then re-insert the sensor. If you want to keep a real cat...you may want to install it yourself and save $$$, it's not very complicated. Hope this helps
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Old 01-21-2012, 09:53 AM   #4
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Default Re: P0420 Code

Some preliminary checks should be done with a scan tool, however the cat is likely bad...
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Old 01-27-2012, 08:59 PM   #5
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Default Re: P0420 Code

To test the Cat..
-get a pryometer and check the temperature of the inlet, compared to the outlet, the outlet should be slightly hotter because of the chemical reaction inside.
-get a rubber mallet and lightly tap the cat, if you hear rattling inside, the honeycomb are broken, time for new cat.
-a bad post oxygen sensor with trigger a bad cat. the post o2 sensor voltage reading should be steady and high, around 800mv. If voltage is low, the cat is not doing the job by storing the oxygen inside, and is leaking, that means cat got a hole in it. Need new cat.
-If you got a decent scanner that can read Mode 6, you can check to see if it's out of parameter.

Hope that helps
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Old 01-27-2012, 09:59 PM   #6
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Default Re: P0420 Code

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To test the Cat..
-get a pryometer and check the temperature of the inlet, compared to the outlet, the outlet should be slightly hotter because of the chemical reaction inside.
Incorrect. Many modern cats have a low OSC and as such the gases are cooler by the time they exit the rear.There is no listings as to what cats are low OSC and which are high, so this testing method may lead one to erroneously replace a good working cat. In addition the PCM is constantly running intrusive tests and the cat may be in a rich or lean state at the time of this test. Also most, if not all modern exaust sytems consists of double walled tubing. This will make an accurate temp reading tough to get. Finally, metal piping has a poor emissivity.,which will also give an inaccurate reading.
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-get a rubber mallet and lightly tap the cat, if you hear rattling inside, the honeycomb are broken, time for new cat.
Uhhh,yeah i suppose one could still do that...
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-a bad post oxygen sensor with trigger a bad cat.
Somewhat true, but very unlikely. The cat monitor will suspend in the event of a failed O2 monitor.
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the post o2 sensor voltage reading should be steady and high, around 800mv. If voltage is low, the cat is not doing the job by storing the oxygen inside, and is leaking, that means cat got a hole in it. Need new cat.
Completely incorrect.
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-If you got a decent scanner that can read Mode 6, you can check to see if it's out of parameter.

Hope that helps
Mode 6 will only show a pass/ fail result at the time of testing. The cat can fail 1 out of 4 times during testing and you would never know whether it is good or not.
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Old 02-04-2012, 10:21 PM   #7
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Incorrect. Many modern cats have a low OSC and as such the gases are cooler by the time they exit the rear.There is no listings as to what cats are low OSC and which are high, so this testing method may lead one to erroneously replace a good working cat. In addition the PCM is constantly running intrusive tests and the cat may be in a rich or lean state at the time of this test. Also most, if not all modern exaust sytems consists of double walled tubing. This will make an accurate temp reading tough to get. Finally, metal piping has a poor emissivity.,which will also give an inaccurate reading.
Uhhh,yeah i suppose one could still do that...
Somewhat true, but very unlikely. The cat monitor will suspend in the event of a failed O2 monitor.
Completely incorrect.

How would you check the catalytic converter? Help the guy out instead of criticizing.
Mode 6 will only show a pass/ fail result at the time of testing. The cat can fail 1 out of 4 times during testing and you would never know whether it is good or not.
How would you check the catalytic converter? Help the guy out instead of criticizing.
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Old 02-05-2012, 10:37 AM   #8
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Default Re: P0420 Code

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How would you check the catalytic converter? Help the guy out instead of criticizing.
Correcting is critizing??



With out a scan tool the guy is hosed. There is not much he can check for other than an exhaust leak. Even with a scan tool,all he is looking for is proper fuel control. (good trims)
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Old 02-05-2012, 07:59 PM   #9
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Correcting is critizing??



With out a scan tool the guy is hosed. There is not much he can check for other than an exhaust leak. Even with a scan tool,all he is looking for is proper fuel control. (good trims)
Didn't mean it that way.

Besides, exhaust leak and disassembling, what other proper procedure would be correct to check if you got a bad cat? You seem knowledgeable. Thanks
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Old 02-05-2012, 09:43 PM   #10
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Default Re: P0420 Code

Other than the code, I've been told that bad cats tend to give the exhaust a rotten-egg smell. I've never had a cat fail, so I can't confirm this from experience, but maybe it will help...
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Old 02-05-2012, 11:12 PM   #11
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Didn't mean it that way.

Besides, exhaust leak and disassembling, what other proper procedure would be correct to check if you got a bad cat? You seem knowledgeable. Thanks
Are you a technician? Do you have access to Alldata or Mitchell? Or an OEM website? I only ask because the trouble shooting steps for a P0420 or P0430 are pretty self explanatory. There are 6 simple steps to follow. This info is good for ANY vehicle regardless of make or model,so long as it is OBD2:



1. Verify the vehicle is in fuel control. (Closed loop and good fuel trims)
2. Verify that there are no exhaust leaks.
3. Check for any related TSBs. Some times there are PCM reflashes available because some PCMs will set false cat codes.
4. Verify that the vehicle has an OE cat. All aftermarket cats will set a cat code on an OBD2 vehicle. Some sooner than later, but all with in 2 years or less from the time of install.
5. Check for proper connection and fit of the rear O2 sensor plug. (a bad connection may not flag an O2 code,but may give false cat code. I have never seen this occur,but it is a possibility that should be checked)
6. Verify there are no other hard or pending codes, if there are, these should be addressed first as they could be setting a false cat code.



The PCM catalyst monitor is the most stringent,accurate monitor the vehicle has. The PCM has one main priority and only one. Everything else is secondary. The PCMs job is to protect the cat. There is no published OE data that indicates that the secondary O2 sensors should be monitored for catalyst deterioration. That is info that has been spread from tech to tech. While some O2 sensors will mirror the front when the Cat is bad, not all do.Honda,Toyota, and Subaru come to mind. Different models will behave differently. It really depends on the type of catalyst being used and the fuel and catalyst monitoring strategy. Some use intrusive testing,others do not.
Also most late model Japanese vehicles use an Air/fuel ratio sensor in front these days. The signals between an AF sensor and O2 sensor are completely different. One is meausred in voltage,the other in current. They would never match up. The 6 steps above are all that is need to confirm the cat is bad. I have replaced 100's of cats following this procedure and it has never failed me. I have never needlessly replaced a rear O2. This procedure was taught to me years ago during training by individuals smarter than me and with much more experience.
I am a CA State smog tech as well as a 15 year ASE Master Tech.
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Old 02-06-2012, 08:14 PM   #12
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Default Re: P0420 Code

Quote:
Originally Posted by DCFIVER View Post
Are you a technician? Do you have access to Alldata or Mitchell? Or an OEM website? I only ask because the trouble shooting steps for a P0420 or P0430 are pretty self explanatory. There are 6 simple steps to follow. This info is good for ANY vehicle regardless of make or model,so long as it is OBD2:



1. Verify the vehicle is in fuel control. (Closed loop and good fuel trims)
2. Verify that there are no exhaust leaks.
3. Check for any related TSBs. Some times there are PCM reflashes available because some PCMs will set false cat codes.
4. Verify that the vehicle has an OE cat. All aftermarket cats will set a cat code on an OBD2 vehicle. Some sooner than later, but all with in 2 years or less from the time of install.
5. Check for proper connection and fit of the rear O2 sensor plug. (a bad connection may not flag an O2 code,but may give false cat code. I have never seen this occur,but it is a possibility that should be checked)
6. Verify there are no other hard or pending codes, if there are, these should be addressed first as they could be setting a false cat code.



The PCM catalyst monitor is the most stringent,accurate monitor the vehicle has. The PCM has one main priority and only one. Everything else is secondary. The PCMs job is to protect the cat. There is no published OE data that indicates that the secondary O2 sensors should be monitored for catalyst deterioration. That is info that has been spread from tech to tech. While some O2 sensors will mirror the front when the Cat is bad, not all do.Honda,Toyota, and Subaru come to mind. Different models will behave differently. It really depends on the type of catalyst being used and the fuel and catalyst monitoring strategy. Some use intrusive testing,others do not.
Also most late model Japanese vehicles use an Air/fuel ratio sensor in front these days. The signals between an AF sensor and O2 sensor are completely different. One is meausred in voltage,the other in current. They would never match up. The 6 steps above are all that is need to confirm the cat is bad. I have replaced 100's of cats following this procedure and it has never failed me. I have never needlessly replaced a rear O2. This procedure was taught to me years ago during training by individuals smarter than me and with much more experience.
I am a CA State smog tech as well as a 15 year ASE Master Tech.
Thanks for the great info.
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Old 04-11-2017, 10:48 AM   #13
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Default Re: P0420 Code

Yes, thanks for the great info.
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Old 04-11-2017, 10:56 AM   #14
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Default Re: P0420 Code

Should be stickied.


Still in this day and age, people are needlessly replacing O2 sensors for cat codes.



The info I posted was accurate then,and is accurate now.
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Old 04-11-2017, 11:29 AM   #15
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Default Re: P0420 Code

My 2010 4 cylinder, 4-door Accord has a warm up three way cat and a under the floor catalytic converter. Are there DTC codes (such as P0420) unique to each, or is P0420 solely reporting on the failure of the under floor cat?
Thanks
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Old 04-11-2017, 12:37 PM   #16
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My 2010 4 cylinder, 4-door Accord has a warm up three way cat and a under the floor catalytic converter. Are there DTC codes (such as P0420) unique to each, or is P0420 solely reporting on the failure of the under floor cat?
Thanks
Only the WU cat is monitored, the undercar cat is not. So there can be no code for the under car cat. A P0420 is a failure of the WU cat.

Additionally there is a service bulletin for your vehicle which describes an issue with the A/F sensor(also referred to as O2 sensor) coming apart and physically damaging the cat internally, which will set a P0420. So you may need one or both sensors in addition to the cat.

TSB# 14-002

(please note that not all 2010s are affected. There is a VIN cut off)
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Old 04-11-2017, 12:57 PM   #17
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Default Re: P0420 Code

Thanks for your help in this. It is much appreciated.
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Old 04-11-2017, 08:35 PM   #18
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Default Re: P0420 Code

test pipe! what cat?! race car!!!
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2003, accord, bad, cat, code, crv, driving, honda, hondatech, o2, p0420, po420, post, reading, sensor, thermostat, voltage

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