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Thread: EGR valve causes Check Engine light to come on 3.1 V6

  1. #1

    Default EGR valve causes Check Engine light to come on 3.1 V6

    I have this 94 Century that has the 3.1 V6 in it.
    I keep having the Check Engine light come on.
    I have a scan tool, so I can find out the codes, and it is always an EGR code.
    It has the digital EGR valve on it with the 3 solenoids.
    It varies as to which solenoid it says has the problem.

    Recently, I took the EGR valve off and took the base apart. I cleaned out all the carbon (there wasn't much anyway) and just made sure things were generally not stuck and the parts inside were free to move.

    However, I continue to get the Check Engine light coming on and it is always an EGR code (P1403, P1404, P1405).

    I don't understand what is wrong here, nor do I know what to check.

    Does anyone have thoughts on this? What might be wrong? What should I check?
    Thanks!



  2. #2
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    I'll check for that tomorrow. For some diagnostic procedure that can help you.
    Quote Originally Posted by mechanizeddeath
    I mean there's a lot more than can go horribly wrong with car than when your iPod dock stops working due to a solder job so bad that my dog could do better.
    " Since little or nothing is known about the principles involved in magneto reluctance, diagnosing faults can be a problem ... "  & " treat all other problems as if they do not exsist . "

  3. #3

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    I forgot to say that the only time the Check Engine light comes on with the EGR code is when I'm decelerating and my foot is off both the gas and the brake. It never comes on any other time.

    It's usually when I'm coming up to a stop sign and I've taken my foot off the gas, but I'm just coasting and haven't put my foot on the brake yet. I'm not usually going very fast, maybe 20 or 25 mph.

    As a matter of fact I cleared the codes today and drove around. After 10 miles, sure enough, the light came back on.

    Thanks for any thoughts.

  4. #4

    Pontiac6ksteawd's Avatar
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    Sounds like a stuck pintle in the EGR valve. May need replacement.. JUNKYARD!
    Brian - Carpe Diem

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  5. #5

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    I thought it might be something like this, so I took the valve apart and made sure everything was clean and parts were free to move. I even put a tiny bit of oil on the moving parts so they wouldn't get hung up. Is there any way to repair this thing?
    This is what I feel like right now

  6. #6

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    After doing some online reading, it appears the problem must be a blocked EGR to intake manifold passage. Everything I've read points to this. Apparently the passage leading from the EGR valve to the intake manifold is narrow and tends to get plugged with carbon on the 3.1. It seems like other people have this situation of the light turning on when they are coasting with their foot off the accelerator. There should be a vacuum drop in the intake manifold, and there isn't one because the passage is blocked. The computer sees this and thinks one of the solenoids is stuck closed, so it sets a code. Looks like I've got some decarbonizing to do.

  7. #7

    Pontiac6ksteawd's Avatar
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    I completely forgot about that. I had the same problem on my 3.1. And BTW, you dont have a 3.1, you have a 3100. Same displacement, completely different breed of motor thou.
    Brian - Carpe Diem

    I dont have to love my president, or any god, to love my country!!
    More people have died in the name of "God" than in all wars combined thruout history
    90 Pontiac ASC McLaren Turbo Grand Prix 128k - 01 Pontiac Aztek GT AWD 96k - 04 GMC Envoy SLT XUV 121k

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    Senior Member Prospeeder's Avatar
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    I had the same issues with my Digital EGR. I did the service manuals OHM tests on each set of pins and 2 of the 3 solenoids failed the ohm test. I tried cleaning and all my passages were clear to no avail. Try getting a cheap multi meter and ill get the specs on monday from school.
    "Pontiac, Of Course"
    1990 Pontiac Turbo Grand Prix 3.1T
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    here's a procedure to check the valve operation:



    and the diagram:
    Quote Originally Posted by mechanizeddeath
    I mean there's a lot more than can go horribly wrong with car than when your iPod dock stops working due to a solder job so bad that my dog could do better.
    " Since little or nothing is known about the principles involved in magneto reluctance, diagnosing faults can be a problem ... "  & " treat all other problems as if they do not exsist . "

  10. #10
    Senior Member Prospeeder's Avatar
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    Theres ohm tests too, i remeber that page on mitchell, just another figure should show the Plug, the pins all letered, and the A-B A-C, A-D terminals and thier respective resistance range. Mine worked, and passed the above test, but failed the electrical test.
    "Pontiac, Of Course"
    1990 Pontiac Turbo Grand Prix 3.1T
    1998 Audi A4 Quattro 1.8T
    1999 Audi A6 Quattro Wagon
    1991 Audi 200 Auto
    1980 VW Dasher Diesel

  11. #11
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    Quote Originally Posted by Prospeeder View Post
    Theres ohm tests too, i remeber that page on mitchell, just another figure should show the Plug, the pins all letered, and the A-B A-C, A-D terminals and thier respective resistance range. Mine worked, and passed the above test, but failed the electrical test.


    Edit: Found the right one a split second later...
    Quote Originally Posted by mechanizeddeath
    I mean there's a lot more than can go horribly wrong with car than when your iPod dock stops working due to a solder job so bad that my dog could do better.
    " Since little or nothing is known about the principles involved in magneto reluctance, diagnosing faults can be a problem ... "  & " treat all other problems as if they do not exsist . "

  12. #12
    Senior Member Prospeeder's Avatar
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    Mine were

    A-D 25
    B-D 12
    C-D 26

    So 2 of my solenoids are junk, now i need to fork out the 80+ dollars my price on one of these things, uhg, why cant they be like the 3300 and just not have an egr....
    "Pontiac, Of Course"
    1990 Pontiac Turbo Grand Prix 3.1T
    1998 Audi A4 Quattro 1.8T
    1999 Audi A6 Quattro Wagon
    1991 Audi 200 Auto
    1980 VW Dasher Diesel

  13. #13

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    Thanks everyone for the responses.
    I took the throttle body and the EGR valve off today, and found that the passage was JAMMED with carbon. I used a wire coat hanger to start off, along with some carb cleaner. Eventually, and I mean after a LONG time, I broke through the passage and used a wire brush to clean it all out.
    The problem is the passage is something like 2 1/2 inches long, and it's as narrow as your pinky, if not smaller, and it has a curve in it.
    And carbon is not very easy to get out without mechanical scraping, which is very hard when the passage opening is down inside the intake manifold.
    But, it's fixed now, so I'm quite relieved.

    By the way, someone said the 3300 V6 doesn't have EGR- really?! How can it not? I thought all cars made since about 1973 ALL had EGR valves for NOx emissions...

    And what is the difference between the 3.1 and the 3100? Yes, I do have the 3100 engine in my car as it says 3100 on the intake manifold. Overall I'm quite pleased with the engine. It really has good get up and go.

    These Buicks are really nice. Good power, quiet, nice seats, good ride, smooth shifting transmission, and they seem to last a long time, too.

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    Quote Originally Posted by sky81 View Post
    By the way, someone said the 3300 V6 doesn't have EGR- really?! How can it not? I thought all cars made since about 1973 ALL had EGR valves for NOx emissions...
    Mine 3300 doesn't. IIRC, they altered the valve timing so that it wouldn't require any exhaust to be recirculated

  15. #15

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    And this is on a U.S. car with Federal (i.e. non California) emissions?
    Not a Canadian car right?
    Wow. If they did that on the 3300, I wish they had done it on more motors. I'm not really a big EGR fan but I figured it was a necessary evil.

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