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  #1  
Old 07-12-2011, 06:40 PM
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DTC code P0420

I have a 2007 dodge charger with 2.7l and 92k on it
I got this code while I was about 2k miles into my vacation
When I got home I erased the code but it came back about a day later
I read some of the posts on this code but there doesn't seem to be any consensus on it

A lot of people are messing with their exhaust system and that is one of the reasons for the code but I did not make any mods to the exhaust

Other say they just turn it off and does not come back after that but mine does

I don't have any other codes and I did not change any of the o2 sensors. Not sure if the previous owner did also not sure when the last tune up was done

I looked at the waveform on the rear oxygen sensor one time and I noticed it was moving quite a lot so I know that's not good but I am not sure what is causing it

Could the o2 sensor be just dirty ? I did a lot of driving in the mountains so a lot of accelerations and decelerations and the light came on later on that day

Would a tune up help or is there anything else I can check before I go ahead and replace the converter ?

Any comments or advice would be appreciated
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Old 07-16-2011, 07:06 AM
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I looked under the car but I did not find anything unusual. There are no exhaust leaks or discolorations on the converter I banged on it and I did not hear any rattling

I had an idea that just came to me after I finished looking under there.
I thought about buying an o2 sensor to see if that would eliminate the problem but then I thought why not just swap it with the one on the other side.
If the wire is long enough I don't see why that could not be done.
I assume they are the same type so it should not make any difference as to where it is installed

If I can swap it and the problem is on the other side now that would prove that the sensor is bad
On the other hand if I swap it and the problem is still there than it's most likely the converter
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Old 07-23-2011, 06:39 AM
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I got the driver side out and it looked pretty dirty not sure how much of that is normal
It had black soot about 1/4" wide band all around the base and a line pf black soot on one side only the rest was somewhat cleaner in the sense that I could see the the metal

Is that an indication of anything ? Maybe the heater in the sensor is not working well or the cat is bad ?
Is there any test I can do on the sensor while I have it out ?
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Old 07-23-2011, 08:47 AM
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How is the car running? Does the code stay on all the time or does it come and go?
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Old 07-23-2011, 03:55 PM
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The car is running fine. When it happened I drove it with the light on all the time back and forth to work for a week Then on the weekend I erased the code and the light was off for one day than the next day it came on and stayed on for the rest of the week
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Old 07-24-2011, 04:43 PM
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I saw a you tube video of a way to test the o2 sensor so I gave that a try while I had the sensor out but I wasn't able to prove anything with that Supposedly if you measure with a volt meter between the signal wire and ground and put the tip in front of a flame to get it up to 600 degrees you supposed to get about 0.9 volts The one they showed was a single wire and I have 4 wires so I am not sure if it's the same type of sensor.
Anyway I measured between the black and the gray wire but I wasn't getting much movement so then I measured between the black and the body of the sensor and I measured about 0.5 volts In the video they say it supposed to go up to 0.9 in less then a minute and after it's out of the flame it should go down in about 3 seconds In the video it went up in about 3 seconds but mine took at least 30 seconds just to get to 0.5v and id didn't look like it was going to go much higher and when I took it out of the flame it took like 20 seconds to go down so I am not sure if that proves anything

After that I decided to do the swap and I swapped the 2 rear sensors from one side to the other and the problem is still on bank 1 so that proves that the sensor is working normally it's just sensing something on bank 1

So it looks more like it's the cat on that side
Is there a way to clean it or perhaps bypass the problem until the cat is really bad not just a little out of spec ?

I read about some extensions that available to move the sensor out of the stream but it seems like they got mixed results so I am not sure if that will work in my case
I also read about some electronic o2 simulators
Did anyone ever try those ?
I am going to look more into that before I replace the cat
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Old 07-30-2011, 06:04 AM
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Here is a strange one
I did an experiment yesterday by wrapping the o2 sensor with aluminum foil and some buss wire just to see if that would make the waveform flat so the p0420 would go away and it did not make any difference. I thought that was weird but than I took the o2 sensor out of the exhaust pipe while still leaving it connected and than I saw the waveform was more random like it was flat for a period of time than it would spike up and than go flat again for a while

This didn't make any sense to me I mean the oxygen sensor is wrapped up and it's not even in the exhaust and it's still sensing something
So then I disconnected the sensor from the plug and then I got code p0058 which I knew I would get a code but that was for sensor 2/2 So than I realized I was working on the wrong bank

Most v8's I worked on cylinder 1 is on the driver side but this v6 or maybe all v6's have cylinder 1 on the passenger side so now I have to repeat the experiment on the other side and see what happens

The strange part is that while I had the oxygen sensor out in bank 2 it affected the waveform for the oxygen sensor in bank 1 How is that possible ?
Does that mean the cat maybe is not quite dead yet ?
I guess I will find out something today
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Old 07-30-2011, 09:28 AM
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I would recommend just replacing the 02 sensor. For $20 its cheaper than the cat!
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Old 07-30-2011, 05:04 PM
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Quote:
Originally Posted by PlumCrazyDaytona View Post
I would recommend just replacing the 02 sensor. For $20 its cheaper than the cat!
I appreciate your suggestion but I don't think that is going to work since I did the earlier experiment where I swapped the oxygen sensors from one side to the other and the problem remained on the same side so that proves that the oxygen sensor is not the problem

Since I know now that bank 1 on the v6 is on the passenger side I took a closer look at it. I banged on it with my fist and I heard some rattling It sounded small like it has some pebbles in there so probably a small chunk broke off in any case that's not good sign and that is probably the cause of the p0420

I repeated the experiment I did on the other side on bank one this time where I had the oxygen sensor wrapped in aluminum foil and than wrapped with buss wire

The experiment worked for a while The waveform was holding steady at about 067 volts So I took it out for a run around the block only about 1 mile or 2 so I can run it at 55mph so the monitors would start running since I erased the code

When I got back I noticed the waveform was around 0.12 volts and was steady for a few seconds then it jumped up and started going up and down although somewhat erratically so I thought maybe the foil fell off
but after I took the oxygen sensor out I noticed the buss wire turned yellow and at the tip where I just twisted the foil it looked like the foil melted so it was only sensing through the small hole at the tip of the sensor and that was still enough to make a big jump on the waveform

I could probably make a better cover to fool the sensor in case I don't find anything else but there is no reason at this point since the cat is more likely the suspect now with the rattling noise
If it was just carbon buildup I would have attempted to clean it with something but if it's breaking up there is no use in cleaning it

So now I have to look around for a new cat
Any opinions as to what type is best ? OEM or after market ? Any particular brand ?
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Old 07-30-2011, 09:02 PM
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I wonder if you could just use some foulers with the 02's? Or maybe a 5.7 cat would work? I dont know I just have two factory ones with under 4000miles
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