4100 service now light
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HT4100 4.1, 4.5, 4.9 Discussion, 4100 service now light in Cadillac Engine Technical Discussion; Hi, I'm new to this forum, but it seems to be the answer to many prayers. I'm the proud new ...
  1. #1
    baldizzone is offline Cadillac Owners Member
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    4100 service now light

    Hi,
    I'm new to this forum, but it seems to be the answer to many prayers. I'm the proud new owner of a mint 1983 Eldorado Biarritz. Well maintained car with 107,000 on its original HT4100. Recently, at highway speed, the "service now" light comes on intermittently. I've noticed no change in performance. As this car is a hobby, I'd like to avoid the GM dealership to read the code. Any ideas before I bring it to a mechanic? The owners manual is vague.

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  3. #2
    serdriver is offline Cadillac Owners Member
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    Re: 4100 service now light

    Quote Originally Posted by baldizzone
    Hi,
    I'm new to this forum, but it seems to be the answer to many prayers. I'm the proud new owner of a mint 1983 Eldorado Biarritz. Well maintained car with 107,000 on its original HT4100. Recently, at highway speed, the "service now" light comes on intermittently. I've noticed no change in performance. As this car is a hobby, I'd like to avoid the GM dealership to read the code. Any ideas before I bring it to a mechanic? The owners manual is vague.
    With the ignition on, but not the car, press the off and warmer buttons. This will put the car in self-diagnosis mode. A series of number codes will be displayed in the climate control panel. These numbers I believe will repeat three times. The last time right them down; these are your "hard codes." Once you get these numbers, either come here and ask what they mean ( I have the Cadillac Serivce manual, so I can tell you) or go to caddyinfo.com and do a search for the codes there. Then you'll know what's wrong and get to fixing the problem.

    Welcome.

  4. #3
    baldizzone is offline Cadillac Owners Member
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    Re: 4100 service now light

    Quote Originally Posted by serdriver
    With the ignition on, but not the car, press the off and warmer buttons. This will put the car in self-diagnosis mode. A series of number codes will be displayed in the climate control panel. These numbers I believe will repeat three times. The last time right them down; these are your "hard codes." Once you get these numbers, either come here and ask what they mean ( I have the Cadillac Serivce manual, so I can tell you) or go to caddyinfo.com and do a search for the codes there. Then you'll know what's wrong and get to fixing the problem.

    Welcome.
    Thanks for the quick reply,

    1983 ht-4100 When put in self-diagnosis mode, it returned:

    ].8.8 16 ].8.8 16 ].8.8 7

    i believe the ].8.8 (the best i can reproduce it with the characters at hand! actually the first symbol of this code looks like a backwards E)
    is a symbol of some sort and the codes returned were 16,16 and 7.

    Please advise if this is worth anything.

    thanks again, Bill

  5. #4
    serdriver is offline Cadillac Owners Member
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    Re: 4100 service now light

    Ok, Bill, here is what the book says.

    -1.8.8 is displayed to indicate the beginning of the diagnostic mode, so this is normal.

    Code 16 is "Generator voltage out of range." There are also two square boxes next to this code. If there are two square boxes next to a code, it means the "Service Now" light will come on, so this is why your light is coming on.

    The 7 is not a code, it tells you that the diagnostic is done and the system is ready for further testing. So, your only problem is 16.

    Good luck. Hope this helps.

  6. #5
    baldizzone is offline Cadillac Owners Member
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    Re: 4100 service now light

    Quote Originally Posted by serdriver
    Ok, Bill, here is what the book says.

    -1.8.8 is displayed to indicate the beginning of the diagnostic mode, so this is normal.

    Code 16 is "Generator voltage out of range." There are also two square boxes next to this code. If there are two square boxes next to a code, it means the "Service Now" light will come on, so this is why your light is coming on.

    The 7 is not a code, it tells you that the diagnostic is done and the system is ready for further testing. So, your only problem is 16.

    Good luck. Hope this helps.
    THANKS
    I guess now I have something to do this weekend. I've had a belt squeal I've been ignoring and I guess its time for a retorqueing or replacement, if that doesn't do it, I'll have the alternator checked out. Thanks for the quick replies, I really apprecciate it. Bill

  7. #6
    carnut is offline Cadillac Owners Master
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    with the engine off, try rotating the alternator pulley backwards against normal rotation. if you can rotate the pulley with your hand the smog pump belt! is too loose. ck the smog pump belt for glazing, wear. if ok tighten the belt. then ck the alternator belt condition and tightness. if you ck the alternator belt, you will see it wraps only around the water pump pulley. if the smog pump belt is loose and slipping the alternator will slip causing belt squeal! i've seen this alot and will lead to improper diagnosis and alternator replacement. hope this helps, Bill. please reply with what you found. thanks.

  8. #7
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    2dfx is offline Cadillac Owners Fanatic
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    Re: 4100 service now light

    Quote Originally Posted by baldizzone
    THANKS
    I guess now I have something to do this weekend. I've had a belt squeal I've been ignoring and I guess its time for a retorqueing or replacement, if that doesn't do it, I'll have the alternator checked out. Thanks for the quick replies, I really apprecciate it. Bill
    Funny enough on my 96 Sierra there was a belt squeal consistent with engine RPM and one day it stopped. As soon as it stopped the Battery light came on informing me that my alternator was shot!

  9. #8
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    Re: 4100 service now light

    Bill,

    as long as we are on this subject, what is your opinion on belt dressings for serpentine bands? i have used them on the "V" belts, but not sure here on the 4100 .. i did spray the new serpentine on my 4100, and seems it has lots more traction but i am wondering if this will reduce the belt life span ...


    Quote Originally Posted by carnut
    with the engine off, try rotating the alternator pulley backwards against normal rotation. if you can rotate the pulley with your hand the smog pump belt! is too loose. ck the smog pump belt for glazing, wear. if ok tighten the belt. then ck the alternator belt condition and tightness. if you ck the alternator belt, you will see it wraps only around the water pump pulley. if the smog pump belt is loose and slipping the alternator will slip causing belt squeal! i've seen this alot and will lead to improper diagnosis and alternator replacement. hope this helps, Bill. please reply with what you found. thanks.

  10. #9
    carnut is offline Cadillac Owners Master
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    hi stealth, carnut here. re: belt dressing in general, i use it only as a diagnostic aid. if belt is sprayed and the noise quits, it means tighten and/or replace the belt. re: spraying on a serpentine belt, it wont harm the belt but same thing applies, if the noise stops, replace the belt. as you know one cannot tighten a serp. type belt. good to talk to you at this forum.

  11. #10
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    Stealth is offline Cadillac Owners Enthusiast
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    Re: 4100 service now light

    good to know that .. it didnt occur to me to use it that way .. i had hoped the dressing would keep the rubber pliable longer ...

    thanks .. i'll be hanging around this forum a bit more often ...

    Quote Originally Posted by carnut
    hi stealth, carnut here. re: belt dressing in general, i use it only as a diagnostic aid. if belt is sprayed and the noise quits, it means tighten and/or replace the belt. re: spraying on a serpentine belt, it wont harm the belt but same thing applies, if the noise stops, replace the belt. as you know one cannot tighten a serp. type belt. good to talk to you at this forum.

  12. #11
    baldizzone is offline Cadillac Owners Member
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    Re: 4100 service now light

    Dear Car,

    I had my mechanic replace all belts. It stopped the squeal and the vibration I had when the compressor is on and the car is idling (he also raised the idle, so he probable cheated on this one). no light (service engine now) for the first few days, now its back. also noticed today for the first time the "service engine soon" light came on for the first time. I'm gonna' check the codes again as well as probably have the alternator and regulator (if not integrated) checked althought the previous owner replaced it within the past 2 years (mabe a bad rebuild). when I get the codes, if there is anything new I will post to try to find out. Thanks

    Bill

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