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P0401 - will it definitely come back?

Discussion in '80-Series Tech' started by SeanAndHis80, Feb 3, 2004.

  1. SeanAndHis80

    SeanAndHis80

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    In a classic Sean moment, I was on my way to get the cruiser inspected when I looked down and saw the CEL. Thanks to this board (as usual) I headed over to Autozone (note to self: it's Autozone not Autobarn where some guy whispered to me that it is Autozone that will read the code) - sure enough it was the P0401 code as has been talked about so much here. He shut off the CEL and the truck passed inspection. Notably, NOX was not tested for - maybe a NY thing.

    The question is: could this be a fluke, or am I to expect the CEL back shortly?
     
  2. Beowulf

    Beowulf

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    >> ... could this be a fluke, or am I to expect the CEL back shortly? <<

    Count on it. :D

    -B-
     
  3. landtoy80

    landtoy80

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  4. SeanAndHis80

    SeanAndHis80

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    I have seen the post, I scoured the posts. I was just wondering if anyone reset the code and did not see it again for a good long time.

    It is pouring out here today, I'll dig into it tomorrow to see if anything obvoius sticks out like the pic you posted...

    Thanks.
     
  5. landtoy80

    landtoy80

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    You can clean the carbon out of the modulator and reset the computer and is will go away for a while.
    If no carbon in modulator then it WILL come back very soon.
    Replace the modulator and keep any more carbon out of the vacuum system.
     
  6. Beowulf

    Beowulf

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    Or, like many of us, you can replace lots of parts and the darn thing STILL came back.

    -B-
    (Hi, My name is Beowulf and I am a P0401-aholic. It's been 13 months and 25 days since my last P0401. Please pray for me.)
     
  7. landtank

    landtank SILVER Star

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    Then again you could just test the modulator per the FSM and determine if it needs replacement at all ::)
     
  8. landtoy80

    landtoy80

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    I think when one part goes bad, the rest goes with it.
     
  9. landtoy80

    landtoy80

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    Testing the modulator doesn't tell you if carbon is getting in it. A pinhole leak might not cause it to fail the test. It didn't on mine. I would clean it out and after several miles it would have carbon in it.
     
  10. SeanAndHis80

    SeanAndHis80

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    LOL - lasted only 9 days. Time to investigate ...after I'm finished with the Honda. I wish there were a board like this one for Hondas. I can't even read the Honda boards, the pages I have read were mostly concerned with Bling!
     
  11. Gundy

    Gundy

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    On our 96 FZJ80 this was caused by carbon buildup in the vacuum
    modulator. I didn't have buildup in the unit but the filter had a spot
    of carbon on the bottom. I cleaned it and reset the CEL . I'm sure it will
    return. I've put about 2000 miles on it since with no return of the CEL.
    I'll be changing the oil soon and I intend to give the filter a cleaning at that time.
    I think this is treating a symptom and not the cause. I suspect some
    other problem is just allowing the carbon buildup.
    For now I just cross my fingers, clean the filter and do the cruiser chant.
    ;)
     
  12. Junk

    Junk

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    Every frickin part of my EGR system has now been replaced as of today.

    Today the EGR valve was replaced and already the truck is running 100% better.
     
  13. landtank

    landtank SILVER Star

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    Maybe it will help with that gas mileage of yours, something had to be wrong there. :cheers:
     
  14. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    [quote author=landtank link=board=2;threadid=10982;start=msg104158#msg104158 date=1076641720]
    Maybe it will help with that gas mileage of yours, something had to be wrong there. :cheers:
    [/quote]

    Diagnosis pertaining to this particular vehicle should be easy:

    LOOSE NUT BEHIND THE WHEEL.... :flipoff2:
     
  15. Eduardo96FZJ80

    Eduardo96FZJ80

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    I too replaced my modulator, and went about 8-10k miles before I saw a re-occurance :rolleyes: then I read one of the -B- post's and............ got a "light" about 2 day's later :mad:

    and I agree with C-Dan's diagnostic analysis of "Junk's" ride :D
     
  16. landtoy80

    landtoy80

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    I think the problem is that the diaphram in the modulator cracks and lets carbon into the modulator. Once carbon is in the vacuum system,depending how long/how much has got into the vacuuum, the rest of the vacuum system will have problems till all the carbon is out.
    I can't see any other way for carbon to get into the vacuum system. The ports on the intake chamber are infront of the air flow of the exhaust gas so all the air that the vacuum sucks is filter by the air filter.
    So if you have more that a couple bits of carbon in the modulator you better remove all the vacuum hoses and VSV to get all the carbon out.


    Junk,I bet your EGR was carboned shut or open as one part of the EGR system was not working for so long that carbon built up on the valve so it wouldn't move.
     
  17. Junk

    Junk

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    While out of principle, I hate to agree with Cdan, I have to in this situation. Still give him the :flipoff2: though. :D

    Well today was test day. Went to DMV for inspection. My HCs are down from over 1,100 to 41 (limit is 100 for passing). So wahoo. No pending code and cleared inpsection. Still have another exhaust leak to find, but the EGR system now looks good. FYI, took off the modulator and looked at the filter.... it was as clean as the sheets on ... oh, never mind :D
     
  18. landtoy80

    landtoy80

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    Junk, do you have the EGR valve? Was it carboned up to where it wouldn't move or only move a little bit?
     
  19. Junk

    Junk

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    Yes, kept valve. It did not look real crapped up, but it clearly was not functioning properly. Kurt, I know you're digging into this more, but this was so bad that it was definitely impacting the way the truck was idling once it warmed up. When the engine was cold, it would idle fine, once it warmed up, it would feel like it wanted to quit.
     
  20. Junk

    Junk

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    One other thing, for anyone that does read this thread (which assumes someone uses SEARCH :D), that big nut is TOUGH to get off.