No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Running
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Running in Past Cadillac Vehicle Discussion; I worked through all the diagnostic codes I was getting and managed to resolve and clear them all (e.g. replaced ...
  1. #1
    nebulosity's Avatar
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    No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Running

    I worked through all the diagnostic codes I was getting and managed to resolve and clear them all (e.g. replaced coolant temp sensor & fixed the ISC circuit problem, etc.).

    So after I cleared the codes, I went to run through the diagnostic codes again with the car running and not running, and in both cases no codes are thrown at all. It goes from -1.8.8 to 0.7 directly all three times. And yet I'm still getting the "Service Soon" and "Service Now" lights. Is this a fluke? Did I not clear everything completely and the service lights have to be cleared separately? I assumed they were directly related (service light == code thrown).

    Considering some values I recorded (below) provided by the ECM during running and not running, is there anything I should look into more thoroughly?

    Here are some sample values I'm getting:

    ENGINE NOT RUNNING:

    -1.8.8 .0.7 (No codes+ready)

    .0.1 8deg (Throttle angle, good)
    .0.2 99kPa (MAP, measuring ambient+agrees w/BARO==good)
    .0.3 99kPa (BARO, measuring ambient==good)
    .0.4 22C (Coolant Temp, measuring ambient==good)
    .0.5 10C (MAT, hmm... that's a bit cold...value is within range but significantly less than ambient... acceptable reading?)
    .0.6 0ms (Injector pulse width.. car not running, good)
    .0.7 0.45V (O2 sensor.. within range... good?)
    .0.8 0deg (Spark advance...car not running, so this is probably an okay value)
    .0.9 1cycles (Number of times engine has been cycled since trouble code last set, sounds good).
    .1.0 0.0V (Battery voltage... shouldn't this read normally even if car is not running?)
    .1.1 0RPM (Engine rpm.. not running, so 0==good)
    .1.2 0MPG (Vehicle Speed.. not running, so 0==good)
    .1.3 16 (PROM ID, within range==good)

    ENGINE RUNNING:


    -1.8.8 .0.7 (No codes+ready)

    .0.1 2deg (Throttle angle, good)
    .0.2 34kPa (MAP, within range+[higher air velocity==lower pressure]==good/expected)
    .0.3 98kPa (BARO, measuring ambient==good)
    .0.4 36C (Coolant Temp, measuring ambient==good)
    .0.5 _N/A_ (MAT, Skipped by accident and didn't record value)
    .0.6 1.6-1.7ms (Injector pulse width, within range==good)
    .0.7 _N/A__ (O2 Voltage, Skipped by accident and didn't record value)
    .0.8 30deg (Spark advance...supposed to be set between 10-20deg... could the service lights be because of this?)
    .0.9 0cycles (Number of times engine has been cycled since trouble code last set, sounds good).
    .1.0 11.5V (Battery voltage... a little low because battery is weak)
    .1.1 880-890RPM (Engine rpm.. Seems like good idle RPM... Could the service lights be complaining about this at all? )
    .1.2 0MPG (Vehicle Speed, stationary==good)
    .1.3 16 (PROM ID, within range==good)

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  3. #2
    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
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    If I had to guess, I'd guess the engine is complaining about the high spark advance. How does it run?
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  4. #3
    nebulosity's Avatar
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Relative to how it ran 10 years ago, I'd say it runs well and actually seems to have more power than I remember, but the knock that it had years ago is 30% more noticeable. I haven't been able to figure out exactly what is causing the knock. I'm wondering about the high spark advance too. Maybe I'll adjust it today until the ECM tells me it's between 10-20 and see if the service lights disappear.

  5. #4
    turbojimmy's Avatar
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Quote Originally Posted by nebulosity View Post
    Relative to how it ran 10 years ago, I'd say it runs well and actually seems to have more power than I remember, but the knock that it had years ago is 30% more noticeable. I haven't been able to figure out exactly what is causing the knock. I'm wondering about the high spark advance too. Maybe I'll adjust it today until the ECM tells me it's between 10-20 and see if the service lights disappear.
    You answered your own question :-). More power is from the advanced timing. But it comes with a price - spark knock.
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    nebulosity's Avatar
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Quote Originally Posted by turbojimmy View Post
    You answered your own question :-). More power is from the advanced timing. But it comes with a price - spark knock.
    At least it's consistent... Now I know what I should adjust.

    And now I really understand why people want/wish to advance the spark timing!

    Thanks for your help!

  7. #6
    csbuckn is offline Cadillac Owners Master
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    I'd say the MAT and O2 test that you skipped on accident while running are important. The O2 test should be a little off with the timing ahead also. The knocking technically should go down a little with the correct timing. Does the light have to be off to pass inspection or does it just not have to have any codes? How did you test for timing? Is this all from the on board computer?
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    nebulosity's Avatar
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Quote Originally Posted by csbuckn View Post
    I'd say the MAT and O2 test that you skipped on accident while running are important.
    Okies, I'll double check the MAT and O2 sensors for sure tonight.

    Quote Originally Posted by csbuckn View Post
    The O2 test should be a little off with the timing ahead also.
    What kind of O2 value will indicate that the result is "ahead"? (eep, sorry for the silly question.. I'm not entirely what the trend is between O2 values and timing.)


    Quote Originally Posted by csbuckn View Post
    The knocking technically should go down a little with the correct timing.
    I'll take a video while I adjust the timing to see how the knock changes.

    Quote Originally Posted by csbuckn View Post
    Does the light have to be off to pass inspection or does it just not have to have any codes?
    Not entirely sure here. I think if the light is on it would be a distraction even if it didn't throw any codes, but maybe it won't be a problem (at least I hope so). What I want to do is have them run their routine without anything making them question whether my car passes. It probably wouldn't be in my favor if they were motivated to do a more thorough inspection or possibly require me to do repairs. I just don't know how picky they will be.

    Quote Originally Posted by csbuckn View Post
    How did you test for timing? Is this all from the on board computer?
    By ear... Adjusted it until the engine idled more smoothly. Afterwards, I checked the value in the on board computer.

  9. #8
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Okay, here's the new data and observations I have (I'll write more later. Hope you can follow..):

    ENGINE NOT RUNNING:
    -1.8.8 30, -1.8.8 30, -1.8.8 30, .0.7 (I'm still getting that 30... ISC Circuit problem)

    .0.2 100kPa (MAP, measuring ambient+agrees w/BARO==good)
    .0.3 100kPa (BARO, measuring ambient==good)
    .0.4 47C (Coolant Temp, measured after it had been idling for about 5 minutes and then turned off)
    .0.5 33C (MAT, measured after idling for 5 mins then turned off )
    .0.6 0ms (Injector pulse width.. car not running, good)
    .0.7 0.45V (O2 sensor.. within range)
    .0.8 0deg (Spark advance...car not running, so this is probably an okay value)
    .0.9 5cycles (Number of times engine has been cycled since trouble code last set, interesting--makes sense I guess).
    .1.0 0.0V (Battery voltage)
    .1.1 0RPM (Engine rpm.. not running, so 0==good)
    .1.2 0MPG (Vehicle Speed.. not running, so 0==good)
    .1.3 16 (PROM ID, within range==good)


    CLEARED THE CODES
    0.0 (result==success).


    ENGINE NOT RUNNING:
    -1.8.8 0.7 (codes sucessfully cleared)

    ENGINE RUNNING:
    -1.8.8 30, -1.8.8 30, -1.8.8 30, .0.7 (Okay, it came back).

    + Econ light is on when entering diagnostics.
    + Off light comes on about 5 seconds later
    + Econ light starts blinking in regular intervals

    .0.4 58C (Coolant Temp, warming up==good)
    .0.5 40C (MAT)

    .0.7 .34 - .35V (O2 Voltage)
    .0.8 30deg
    .0.9 0cycles (Number of times engine has been cycled since trouble code last set, sounds good).
    .1.0 11.2V (Battery voltage... battery is weak)
    .1.1 820-830RPM (Engine rpm)

    .9.5 Engine idled down... rough idle. Car vibrates a bit.

    I Shut Off the Engine

    Adjusted the distributor (from the center of the point where wiring harness is connected, I probably moved it about 6mm counter clockwise)

    ENGINE RUNNING:
    -1.8.8 30, -1.8.8 30, -1.8.8 30, .0.7 (It's still there.)

    + Econ light is on when entering diagnostics (again)
    + Off light comes on about 5 seconds later (again)
    + Econ light starts blinking in regular intervals (again)

    .0.4 92C - 94C (Coolant temp)
    .0.5 63C - 67C (MAT)
    .0.7 0.45V, 0.78V, 0.64V, 0.82V, 0.85V, 0.52V (O2 voltage bounced around)
    .0.8 30 deg (spark advance... still?? I would have thought my adjustment changed this.)
    .0.9 1cycle (since throwing a code)
    .1.0 10.8V - 11.1V, Settled to 10.8V - 10.9V after five minutes of running (battery voltage... need to charge)
    .1.1 820-840RPM, jumped to ~1100 when pressing gas pedal lightly (engine RPM)

    Exhaust smells normal to me. Light burn exhaust smell.. appearance is a little cloudy, could be partially cloudy because of steam; it's cold in Scotts Valley right now. Not much condensation. No real fuel smell in exhaust. No strange burning smells at tailpipe. Everything appears normal.

    Vaccum system tests
    + good vacuum at PCV valve and skinny air cleaner hose.

  10. #9
    csbuckn is offline Cadillac Owners Master
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    The first thing that comes to mind is that the battery is really weak and can't get above 11.2v. My first move would be to charge the battery to full. Next, I'd let it get to full operating temp for the next text. This way the fuel isnt getting adjusted as the temp goes up. Then I'd try to get the computer to pickup the timing change. I wouldn't put much thought into the O2 sensor until the timing issue was solved. Is the ISC motor still acting up? This is just stuff I'd do with that info. The service manual may tell you different. Did you put a vacuum gauge on it or listen/feel for vacuum?
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  11. #10
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Quote Originally Posted by csbuckn View Post
    The first thing that comes to mind is that the battery is really weak and can't get above 11.2v. My first move would be to charge the battery to full.
    Yep. Battery is charging as we speak.

    Quote Originally Posted by csbuckn View Post
    Next, I'd let it get to full operating temp for the next text. This way the fuel isnt getting adjusted as the temp goes up.
    The second and third diagnostics were rn when the engine was above 90C, and "operating temp" is ~85C right?

    Quote Originally Posted by csbuckn View Post
    Then I'd try to get the computer to pickup the timing change. I wouldn't put much thought into the O2 sensor until the timing issue was solved.
    My husband and I decided we should time everything properly with a timing light, and we're doing that tomorrow morning. Hopefully that will resolve the issue and the computer will read something other than 30 degrees for spark advance.

    Quote Originally Posted by csbuckn View Post
    Is the ISC motor still acting up?
    Yes. I think that's why I'm still getting service lights. I'm going to see if I can have my husband help me with the diagnostic flow chart on the 30 code tomorrow (someone needs to watch the ISC motor while the other works the diagnostics panel).

    Quote Originally Posted by csbuckn View Post
    This is just stuff I'd do with that info. The service manual may tell you different. Did you put a vacuum gauge on it or listen/feel for vacuum?
    Yes, but only by feel -- not with a guage. The two places I thought to check tonight were the PCV valve and the vacuum hose the connects to the bottom of the air filter housing. Both had nice vacuum. Where else should I check? I'll see if my harbor freight (lol) compression tester/gauge can also check the vacuum system... I might try to hook that up.

    Wow, I'm exhausted. I have an early day ahead of me. o__o

  12. #11
    csbuckn is offline Cadillac Owners Master
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    Cool, I didn't realize 85* was operating temp. I wouldn't worry about the vacuum gauge thing, I was just wondering if the needle was staying steady or if it was bouncing back and forth. You say that battery was the old one from years ago? I don't know if it will make full charge.
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Quote Originally Posted by csbuckn View Post
    Cool, I didn't realize 85* was operating temp. I wouldn't worry about the vacuum gauge thing, I was just wondering if the needle was staying steady or if it was bouncing back and forth. You say that battery was the old one from years ago? I don't know if it will make full charge.
    The battery is one we bought last year, but it's done a lot of sitting in the last year, so it doesn't hold a charge for too long. We have a warrenty on it and will remedy it later.

    On my way to work on the Caddy. Yay 7am.

  14. #13
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    So we timed everything properly at 10 deg spark advance. Idle went from 880 to about 750rpm. Checked the ECM and its still reading 30 degrees spark advance. I wonder why it hasnt changed. Good news though... spark knock is gone!

  15. #14
    Cadillacboy's Avatar
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    This is good news indeed , I am not expert by any means but I would not skip any details even if sounds stupid because sometimes devils are in details . Well, what kinda fuel are you using ? As far as I am concerned may be type of fuel premium vs regular might cause some weird issues as well
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  16. #15
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    Re: No Codes Thrown, but "Service Soon" and "Service Now" Lights are Lit While Runnin

    Quote Originally Posted by Cadillacboy View Post
    This is good news indeed , I am not expert by any means but I would not skip any details even if sounds stupid because sometimes devils are in details . Well, what kinda fuel are you using ? As far as I am concerned may be type of fuel premium vs regular might cause some weird issues as well
    Premium fuel only. I've never put anything else in it, even 10+ years ago when I started driving it for the first time. (back then, fuel was $1.50/gal for premium....lol)

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