90 S4 Window Electrical Problem
10-21-2008, 12:49 AM
#136
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Bill - 32-35 are all wrong... Unplug all the window controller connections. On the loom plug side test ohms to ground between each of the motor connections 32, 33, 34 & 35.
I think you may find that 32 is shorted to ground and this seems to be the problem. All of these should be floating to ground (infinite ohms)
Alan
I think you may find that 32 is shorted to ground and this seems to be the problem. All of these should be floating to ground (infinite ohms)
Alan
And I don't know about that "cut 38 from 33" thing; seems like an unnecessary wild variable at this point. Is there still a good reason for this connection to be broken? We really don't know what that connection does, so it just seems to throw the possibility of more complexity and randomness into the mix.
I'm back home again and writing up some further ideas for tomorrow.
But I'd really like to hear the result of checking 32 to ground and the possibility of a short there.
Remember, Bill, the outputs to the motors from the controller are nice and straight forward: there are supposed to be no other connections to anything (including ground): just a straight shot to the motor terminals, neither of which is grounded elsewhere.
Hope you guys are willing to share a virtual drink when this one is resolved!
10-21-2008, 01:40 AM
#137
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Yes. The detached sunroof motor will run forever and the passenger window will go down if 33 is connected to 38. CVutting it is the only way I can have the controller connected and not have the sunroof and passenger window running haywire. I will reconnect it in the morning and TRY to run these tests again. [LATE EDIT: No. I just did what Alan suggested...read on]
Last edited by Bill Ball; 10-21-2008 at 02:28 AM.
10-21-2008, 01:47 AM
#138
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Bill - 32-35 are all wrong... Unplug all the window controller connections. On the loom plug side test ohms to ground between each of the motor connections 32, 33, 34 & 35.
I think you may find that 32 is shorted to ground and this seems to be the problem. All of these should be floating to ground (infinite ohms)
Alan
I think you may find that 32 is shorted to ground and this seems to be the problem. All of these should be floating to ground (infinite ohms)
Alan
10-21-2008, 01:49 AM
#139
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Yes. The detached sunroof motor will run forever and the passenger window will go down if 33 is connected to 38. It's the only way I can have the controller connected and not ahve everything running haywire. I will reconnect it in the morning and TRY to run these tests again.
This is starting to look very promising!
I'm going to hold off on my other post until we hear more about this.
To be clear: hyphothesis is that pin 32 (BK/BL wire leading to sunroof motor) is shorted to chassis ground somewhere. Check as Alan stated in post #135.
And if you find the short we're hoping for, make sure to restore the 33/38 connection before doing a follow-up full systems check.
10-21-2008, 01:54 AM
#141
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Now the fun begins. I'll pull the driver seat and check close to that end and then check back from T42 as far as I can. If it buried deep in the harness I may just bypass it.
THANKS TO ALL THE CONTRIBUTORS FOR STICKING WITH ME, AND SPECIAL THANKS TO ED AND ALAN WHO WENT WAY BEYOND EXPECTATIONS TO FIGURE THIS OUT.
Next up - How do I determine why is the blower motor blowing fuses???
THANKS TO ALL THE CONTRIBUTORS FOR STICKING WITH ME, AND SPECIAL THANKS TO ED AND ALAN WHO WENT WAY BEYOND EXPECTATIONS TO FIGURE THIS OUT.
Next up - How do I determine why is the blower motor blowing fuses???
10-21-2008, 02:00 AM
#143
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While you're doing that, I'm going to go upstairs and reassemble mine so it's ready to drive tomorrow (haven't had it out since I detailed it about a week ago and then decided to do some other maintenance on it).
BTW, this was actually very satisfying from my perspective. Lots of crummy stuff going on right now on my end. Nice to participate in something challenging that seems finally to be working out well.
I also appreciated the opportunity to learn more about this particular system; hadn't really been into it much before other than to replace a corroded window motor (but never really had occasion to dig into the circuitry).
We also left a good audit trail for the next poor sap who has to diagnose a problem with this system!
Last edited by Ed Scherer; 10-21-2008 at 02:30 AM.
10-21-2008, 02:16 AM
#145
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Oh, it's no joke. And the problem is the AC was electrically VERY flaky, randomly showing no or very low voltage at the freeze switch (depsite known good headunit), before it settled down to blowing that fuse as soon as the AC is turned on. So, we'll start with the blower motor and see what happens. But I'm encouraged that you guys nailed down the sunroof harness short. The AC should be a piece of cake compared to this.
Ultimately, had I stuck to testing the controller's motor outputs, we could have found the 32 short a long time ago, but the red herrings had me fishing elsewhere.
Ultimately, had I stuck to testing the controller's motor outputs, we could have found the 32 short a long time ago, but the red herrings had me fishing elsewhere.
10-21-2008, 02:30 AM
#147
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Oh, it's no joke. And the problem is the AC was electrically VERY flaky, randomly showing no or very low voltage at the freeze switch (depsite known good headunit), before it settled down to blowing that fuse as soon as the AC is turned on. So, we'll start with the blower motor and see what happens. But I'm encouraged that you guys nailed down the sunroof harness short. The AC should be a piece of cake compared to this.
Ultimately, had I stuck to testing the controller's motor outputs, we could have found this a long time ago, but the red herrings had me fishing elsewhere.
Ultimately, had I stuck to testing the controller's motor outputs, we could have found this a long time ago, but the red herrings had me fishing elsewhere.
My car is back to normal again (15 minutes to remount the controller, button up, and put the test equipment and tools away). And now I can go to sleep in peace (it's getting late here).
I'll be looking for that "AC electrical problems" thread. And perhaps maintaining a safe distance.
10-21-2008, 05:43 AM
#150
Bill, Alan and Ed.
Congratulations on some great diagnostic troubleshooting. I was temped to jump in, but been a little busy to get out all my electrical drawings, manuals etc and start hunting along with you. "Too many cooks can spoil the broth".
Great result and look forward to hearing where the "earth' was.
Bill, I have done quite a bit of fault finding in the HVAC circuity, so when you start up your new thread, hope that I can jump in and help.
Bill, I drop in a post on "WOT" which you may find of interest as it deals with a manual diagnostic procedure in lieu of Hammer, Spanner etc.
Tails 1990 928 S4 Auto
Congratulations on some great diagnostic troubleshooting. I was temped to jump in, but been a little busy to get out all my electrical drawings, manuals etc and start hunting along with you. "Too many cooks can spoil the broth".
Great result and look forward to hearing where the "earth' was.
Bill, I have done quite a bit of fault finding in the HVAC circuity, so when you start up your new thread, hope that I can jump in and help.
Bill, I drop in a post on "WOT" which you may find of interest as it deals with a manual diagnostic procedure in lieu of Hammer, Spanner etc.
Tails 1990 928 S4 Auto