[s-cars] Electrical draw/weirdness after shutdown

[Chad Clark]

Graydon, I'm almost positive I've got your answer. In fact, I've replied to
many s-listers with 1992 MY in the last few years concerning this issue.
Lots of pulling my hair out digging for this one. The problem is indeed your
Central Vacuum Motor (CVM) located next to the battery. It has one or two
vacuum hoses going to it and one electrical connection.  It seems to only
affect the '92 S4 and 100 model cars and possibly early production '93's.
When I bought my S4, I had the exact same symptoms as you have described. Do
you ever hear a clicking relay noise under the drivers kick panel after the
car is shut off?  This CVM controls the power window switches/door locks. I
don't know what fails internally in this component(sounds like you've
already had it apart and know more than I what's involved) There was a
letter in the members correspondence section in the Quattro Quarterly about
3-4 years ago that alluded to this faulty CVM as the problem in a '92 100.
Same problems as you and I. If you can find back issues, I highly recommend
reading and finding this issue.

The cure is to find a later model CVM from an A6/S6 as they updated/upgraded
this part from the early cars('92 vintage) IIRC, last letter on the part# is
a J('92) or B('94>). Just make sure it's from a '94 or later car. I found a
used A6 unit in a salvage yard for $150. Cured all those annoying battery
drains/electrical issues and allowed me to keep my hair:-) HTH,

Chad Clark '92 S$


on 10/14/02 3:01 PM, Graydon D. Stuckey at graydon at elektro.cmhnet.org wrote:

> Hi guys,
>
> I hope someone has diagnosed this problem before.  I am confident that I
> will find this gremlin but I am not too proud to ask for help.  :-)
> Actually, my pride is tired of crawling around under my car.  My car ('92
> S4) has a residual draw after shutoff that can drain the battery in a couple
> days.  I have placed a current shunt into the negative battery cable that is
> rated for 100 amps, and I am monitoring the current draw with my voltmeter.
> I've tracked down a few other unrelated(?) electrical issues and fixed them,
> but this one last major one still eludes me.
>
> Right now, the car is not drawing an unreasonable current draw and it
> appears to be working properly, however, only an hour ago it acted
> strangely, drawing over 50 amps for a few moments.
>
> When it draws, the power window control module clicks on and off.  When on,
> it draws current, and when off, it seems to drop down close to zero.  Then
> if you touch the door lock switch, it will stop.  Oddly enough the door lock
> switch is one thing that still doesn't respond.  The key works with the IR
> sensors, and the alarm sets itself but if I try to lock or unlock the doors
> from the door lock switch, nothing happens.  Now that I have typed this, I
> wonder if a previous troubleshooter has moved the wire from that door lock
> switch to something in the power window circuit by mistake.  I need to trace
> that a little more carefully.
>
> I did remove the power door lock, interior lights and IR remote module which
> includes the vacuum motor, beside the battery.  I took the two PCBs apart,
> and checked every diode.  I took one enclosed relay off, and checked it out.
> The other relays I cleaned with contact cleaner, and I changed a 100uF
> capacitor just in case it was getting leaky.  Then I resoldered the boards
> back together.  I don't think it helped any though.
>
> I might do the same next with my power window module.
>
> Any ideas?  Thanks in advance.
>
> Later,
> Graydon D. Stuckey
> http://elektro.cmhnet.org/~graydon/
>
>
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