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Old 05-30-2012, 12:42 PM   #1
cesargjr
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Question Recurrent P0420 Code.

Hi
Somebody help me with this problem, my malibu is throwing this P0420 code since few months ago. I made like 10 visits to 2 different chevy dealership,
and they just gave up (I know, they shouldn't, but that's basically what they did).
First time I took my car to dealership there was another codes, dont remember what codes were, but something about a sensor on the head, it was just a wiring problem and the other code was a misfire one.
They repaired the sensor wiring and cleaned the injectors, those codes never came back, but after a day and a half P0420 code was back.
After that, they found an oil leakage on a head cover, it was replaced because they told me the code could be caused by a vacuum loss, it didnt solve P0420 code. Then they found an exhaust leak right after a cat, this time I thought we finally got the solution, but it wasnt neither.
They were not able to determine if the catalytic converter was damaged or they just didnt want to take any responsability to fix my car's problem.

At this point, I didn't realized that my car acceleration wasn't like it was before until I drove another malibu, a takeoff on my car was uneven and I had to press really hard the throttle to pass another car. So I read about some damaged cat converter symptoms and causes, one of them was a constant misfire condition. I looked on ebay for a catalytic converter and they were expensive. So I decided to take them off, both. I followed this "tutorial"
http://www.g6ownersclub.com/forum/showthread.php?t=8686
to remove them and used some oxygen sensor spacers from ebay to solve the P0420 and P0430 codes that would be caused by the lack of cats.

This way, my car recovered the throttle response it used to have. But,
again, the P0420 code was there. P0430 don't. So I suppossed the P0420 is still caused by another issue that hasn't been solved.

I got a bluetooth obd interface to analyze the cause of this recurrent P0420.
I read about oxygen sensor readings and after analyzing the O2 sensors levels I think I found something.

I saw in the last freeze frames that the check engine light always came while I was at 0 MPH, at about 800 rpms, braking on D (I remembered that part, check engine always appeared while I was waiting for a green light).

I used Live Data Graph on ScanMaster software to take some O2 sensors readings and found some unstable behavior exactly on bank 1 sensors, just when my car was at idle. But when I revved it (3000-4000 rpms) the readings became little by little as stables as the sensors on bank 2 (they seem to be OK).

Have some screenshots to show you what I mean.
Any kind of help will be really appreciated!
Thank you in advance!

Sorry, not a good english.


Freeze Frame Screenshot


Live Data (while I was taking the sensor readings)


Sensor Readings (1-50 Seconds, Idle)


Sensor Readings (50-100 Seconds, Idle)


Sensor Readings (100-150 Seconds, Idle)


Sensor Readings (150-200 Seconds, Started to Rev)


Sensor Readings (200-250 Seconds, Revving)


Sensor Readings (250-300 Seconds, Revving)
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Old 05-30-2012, 01:08 PM   #2
greenman
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Default Re: Recurrent P0420 Code.

Very simple. The switching on bank 1 sensor 2 is out of limits & setting the 420. Other than that, I know nothing about your modding of the vehicle emissions control system.

Last edited by greenman; 05-30-2012 at 10:53 PM.
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Old 05-30-2012, 01:29 PM   #3
cesargjr
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Default Re: Recurrent P0420 Code.

Quote:
Originally Posted by greenman View Post
Very simple. The switching on bank 1 sensor 2 is out of limits & setting the 420. Other than that, I known nothing about your modding of the vehicle emissions control system.

Bank 2 Graphs seem to be OK, but I have no idea what is causing
that unstable reading in Bank 1 Sensor 1 graph. Once it gets stable
(by revving) sensor 2 does too. I think there's something bad in one cylinder on this bank. I dont have any modding on this vehicle, just no cats and those spacers. Cold air intake temporarily removed due to this situation.
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Old 05-30-2012, 03:20 PM   #4
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Default Re: Recurrent P0420 Code.

I don't know anything about those oxygen sensor substitutes/spacers but it appears as if the bank 2 sensor spacer is working ok. Tried swapping them around?
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Old 05-30-2012, 03:40 PM   #5
cesargjr
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Default Re: Recurrent P0420 Code.

Quote:
Originally Posted by greenman View Post
I don't know anything about those oxygen sensor substitutes/spacers but it appears as if the bank 2 sensor spacer is working ok. Tried swapping them around?
Tried that before, CEL still appeared.
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Old 05-30-2012, 06:27 PM   #6
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Default Re: Recurrent P0420 Code.

Quote:
Originally Posted by cesargjr View Post
Tried that before, CEL still appeared.
OK the CEL came on...I'd expect that but maybe with a 430 code instead because the problem is now in bank 2?

Last edited by greenman; 05-30-2012 at 09:23 PM.
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Old 05-30-2012, 06:39 PM   #7
cesargjr
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Default Re: Recurrent P0420 Code.

Quote:
Originally Posted by greenman View Post
OK the CEL came on I'd expect that but maybe with a 430 code instead?
Code was a P0420, it seems the spacers are not the problem here, both are working fine, something else is causing this code.
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Navigation: Iphone4 w/Navigon (DisplayOut & Resupported)
Kensington LiquidAux Bluetooth Receiver (Hidden inside the lighter compartment)
Cold Air Intake
Air Intake Resonator Removed
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Old 05-30-2012, 07:20 PM   #8
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Default Re: Recurrent P0420 Code.

The one problem I am seeing is the tutorial you followed was for the 2.4L 4 cylinder. Did you find out if this was proven to work properly on the 3.6 that you have? The PCM is very sensitive to changes and something may be off just enough for it to be setting the code. It is hard to diagnose because of the modifications made. It is hard to rule that out as being a possible source of the problem.
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Old 05-30-2012, 09:29 PM   #9
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Default Re: Recurrent P0420 Code.

Quote:
Originally Posted by cesargjr View Post
Code was a P0420...
Then I have no idea, sorry.

Last edited by greenman; 05-30-2012 at 10:49 PM.
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Old 05-30-2012, 10:57 PM   #10
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Default Re: Recurrent P0420 Code.

Quote:
Originally Posted by cesargjr View Post
I dont have any modding on this vehicle, just no cats and those spacers.
Hollowing out the cats is considered a pretty major vehicle mod. It's illegal in most parts of the US.
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