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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1999 STS - engine cooling fans problem in Past Cadillac Vehicle Discussion; just some doubts about the measured outcome: did you use a voltmeter or a testlight? did you unplug the fan ...
  1. #31
    el_dorado_mex's Avatar
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    Re: 1999 STS - engine cooling fans problem

    just some doubts about the measured outcome:

    did you use a voltmeter or a testlight?

    did you unplug the fan connector or penetrate the cable?

  2. #32
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    I used a testlight and I penetrated the wire sheathing.

    AND I did the tests at the same time keeping the ground clip in tact.

  3. #33
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    Re: 1999 STS - engine cooling fans problem

    ok, then we're getting somewhere now...

    your system is working properly, i'll explain:

    low speed operation means fans in series, current flowing through rh fan and then lh fan to ground. therefore you see voltage on both wires on rh fan, which actually is 12v going in and 6v coming out. since you used a test light it will show "hot" at each wire, no matter if 6v or 12v. lh fan has 6v going in and 0v coming out. so what you observed makes sense for low speed.

    disconnecting ect triggers high speed, therefore each fan has its own ground, 12v going in and 0v coming out. so again, what you observed is conclusive.

    now here's my guess: rh fan is somewhat stuck and 6v is not enough to make it spin. i'd say give it a try and spin it a bit, you may feel that it wants to turn, but just not strong enough. or spin it switched off and check if it's hard to turn...

    hope my conclusions are logical, somebody else has an idea on that?

    edit: corrected one "lh" to "rh"

  4. #34
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    I totally understand...however, what puzzles me is that on all of the schematics that I have seen, they show the fan1 relay is FIRST feeding the LH motor (driver's side) and then it goes through the S-P relay then to the RH motor. My system seems to be the reverse of this...the RH motor is getting current in and sending it out; and the LH is getting it in and going to ground.

    You may be "right on" concerning the blade possibly being partially stuck. It doesn't seem to spin as freely as the LH fan and it does make a minor noise when spun in reverse. It also makes sense that this impedance, however, is not enough to stop the HIGH speed operation! Does this mean I need to replace the entire dual fan unit?

    Need to add: I need to check the voltage going in and out of the RH fan because it seems like the LH fan is getting all of the current, not just 6 volts. I say this because the LH fan SEEMS to be running in HIGH speed. Could there be something wrong with the RH fan whereby it is not taking in ANY of the current but simply passing it on to the other fan?

  5. #35
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    Re: 1999 STS - engine cooling fans problem

    regarding the diagram that jimd posted current goes first through the rh fan...

    i think the motors are available seperatly, so just change out that one, or get a known good one (junkyard or friend), or switch yours, so you'll see if the problem switches to the other fan, indicating a lazy motor.

  6. #36
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    I stand corrected. That is the third diagram I have seen but the only one that shows the RH as the first fan. I will see what I can do regarding the RH fan. Thanks ever so much for your help and patience. I hope that you have found the problem. I will report back with my results.

    I tested the voltage: when the ECT is unplugged, BOTH fans are getting IN just under 14V and BOTH are running on high. When I plug the ECT back in and put the ac on, the RH fan is getting IN just over 14V and releasing OUT the same 14V and not working; the LH fan is getting the 14V and is on high speed.

    So is it the motor or connector or something else?

  7. #37
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    Re: 1999 STS - engine cooling fans problem

    14v is weird... that means your cooling fan 1 relay is stuck close, or the wiring from there to the fan is short to +. if the relay was stuck, the lh fan would run all the time actually, so it's not that. you may check the following:

    with only one fan working, check the 87 port at the cooling fan 1 relay for voltage. there should be like 6v to ground.

    and with engine switched off check the resistance between outcoming contact rh fan and incoming contact lh fan (connnectors off the fans). should be continuous.

    could still be the motor, but with 14v present at the ground wire for the rh motor, i'm not that positive about it anymore...

    maybe the low speed switched ground (the one going to the pcm) is short to cool fan 1 relay ground also (which only should be high speed), triggering both relays (but not the middle one) at low speed...

  8. #38
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    I did test the 87 port of fan1 relay and got 14.1V. I also tested fan2 relay and got 14.1V.

    Both fans have continuity

    I am looking at JimD's diagram...fan1 relay appears to be associated with the LH fan, and fan2 relay associated with the RH. The other relay is the S-P. Just making sure I tested the correct ones.

    It seems like the RH fan is not getting any ground when in serial mode. I do see where it gets grounded (via the S-P relay) when in high speed mode. In low speed mode, it appears to get grounded via the LH fan Right?

    I'm trying to understand your last sentence.

  9. #39
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    Re: 1999 STS - engine cooling fans problem

    ok, so there is the problem, exactly, the rh fan doesn't get ground on low speed. both relays are related to both fans, and the middle one just switches ground for the rh fan in high speed mode.

    with continuity i meant not the motors, but the cable between the both motors, the pin coming out of the rh fan and the pin going in at the lh fan, while fans switched off (ignition off). that's for knowing if the middle relay is in the correct position for low speed mode (in other words, checking the series operation).

    try to take out cooling fan 1 relay while one fan is working (low speed), it's just a try, maybe i'm right with this relay getting switched on low speed (that's what i meant with grounds shorted). what happens is that the rh fan gets battery+ from somewhere, while it's supposed to "deliver" what's "left" of current and voltage, to the other fan, which, btw should be running high speed at this moment...

  10. #40
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    Re: 1999 STS - engine cooling fans problem

    I cannot get "one fan" working (low speed)...when only the one works, it is in high speed.

    I also just checked the continuity between the wires connected to the fans. They have continuity.

  11. #41
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    Re: 1999 STS - engine cooling fans problem

    Quote Originally Posted by palidin1029 View Post
    I cannot get "one fan" working (low speed)...when only the one works, it is in high speed.
    that's what i meant, since it's getting 12v, not the 6v meant to be.

    ok, then the middle relay is ok in low speed position. try taking out the cooling fan 1 relay while only one fan works, maybe that leads us to having both fans on low speed...

  12. #42
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    Re: 1999 STS - engine cooling fans problem

    Interesting!!! When I removed fan1 relay, it made no difference. The LH fan kept spinning and the RH kept off. HOWEVER, I put fan1 relay back in its socket and decided to remove fan2 relay to see what happens. When I did, the LH fan stopped...so no neither fan ran. BUT, when I pushed the relay back in the socket, BOTH fans kicked on. I did this several times.

    So the only way to get the RH fan to go on is to remove the fan2 relay and put it back in.

    Another note: when I turn the engine off and then on, we are back to having only the LH fan running on high.

    So do we have a PCM problem? Or a relay problem?

  13. #43
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    Re: 1999 STS - engine cooling fans problem

    pcm is fine i think.

    relay and/or wiring/contacts. it's difficult right now for me to tell what's going on, just plenty of possibilities.
    when both fans work on low speed, what's your voltages at the fan motors, where you had 14v at both pins rh fan and 14v/0v at the lh fan?

  14. #44
    JimD is offline Cadillac Owners Connoisseur
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    Re: 1999 STS - engine cooling fans problem

    Quote Originally Posted by palidin1029 View Post
    ....So do we have a PCM problem?
    Highly unlikely.
    Or a relay problem?
    That's where my money is.

    I suggested 'borrowing' relays in post #23. Did you ever try that? You have not responded one way or another.

    Corrosion or damaged contacts in the relay box are not unheard of. AFTER you disconnect the battery, you can the remove the top section of the fuse/relay panel and take a close look. I would not go poking in there with a nail file or anything else before I completed a systematic eye ball inspection. If corrosion removal is needed, liberal application of electrical contact cleaner followed by repeated insertion/removal of relay blades will eliminate the problem.

    But back to post #23 and borrowing relays as a much easier step.

  15. #45
    palidin1029 is offline Cadillac Owners Member
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    Re: 1999 STS - engine cooling fans problem

    el dorado: I show 13.4 V at each fan after I remove and then replace relay2. Because I just bought the car, I am not familiar with the two sounds of the fans (low and high speeds). However, because of the voltage being 13+, I assume they are on high speed.

    JimD: I did respond regarding the fuses...but not the relays. The fuses are OK. I should be able to switch some of the 4-pin relays but I don't think I have another 5-pin. I can go out and buy one.el dorado:

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