[s-cars] Sunroof in need of exorcism

[Paul Heneghan]

I am now the proud owner of a possessed sunroof!

It's on a UK spec 1995 S6 I'm sure it's identical to A6 models from about
1994 to 1997 - it's got a preselector potentiometer (and some kind of ECU)
instead of a simple open/close switch.

Here are the symptoms:

I started the car on Friday night (the battery is on its last legs and the
engine did turn over quite slowly) and to my surprise the sunroof opened
fully.  The control knob was in the closed position at the time.  Turning
the control knob to open just made clicking noises.  Turning the knob to the
tilt position closed the sun roof a couple of inches.  As the temperature
was 0C, this was not good.

I drove the car home, and then decided to remove the battery to charge it
overnight.  I was hoping that the sunroof ECU had got confused by the lowish
battery voltage.  Just before I physically removed the battery from the car,
I reconnected the terminals briefly, tried the sunroof control and this time
it closed.  Delighted with myself for being so clever, I brought the battery
inside for charging.

A hygroscope showed that 4 cells are fine, one is marginal, and one is not
holding charge properly.  Still, I think it's the original battery - not bad
life.

This morning, I reinstalled the battery.  I started the car and guess what -
the wretched sunroof opened.  This time, it wouldn't close at all no matter
what position the control knob was in.  It just made clicking noises.  I
only wish I'd removed the fuse - I never use the sunroof anyway!

Removing the fuse was non-trivial.  I assumed it would be in the panel at
the side of the dash - the one marked 'sunroof' amongst other things.  It
wasn't!  In fact I never found it.  Searching through the Bentley (I don't
really like the CD-ROM one - a paper copy is SO much easier to use), I
eventually discovered that American models use a circuit breaker which may
or may not be in 'Auxiliary Relay Panel I', the location of which I have no
idea - there are no guarantees that UK models follow the same wiring scheme
anyway!  The Haynes manual has a paragraph that says the sunroof mech. is
FAR to complicated for stupid little DIYers to attempt to understand, and
that I should bring my car to an Audi dealer and give them loads of money -
I'm getting increasingly annoyed with Haynes tendency to recommend the
dealers for anything more complicated than inflating the tyres!

However, I opened the little compartment that houses the sunroof motor and
tried to use the Allen key to close the sunroof manually , but the mechanism
was seized.  I undid the three bolts that hold the motor/gearbox mechanism
in place, and that freed up the mechanism so that I could then reattach it
and use the Allen key to close the sunroof (you've got to push the Allen key
receptor into a recessed position to decouple it from the gearbox so it can
be turned).  Then I disconnected all the connectors that had anything to do
with the sunroof and put everything back together.

I spent a couple of hours tonight pouring over the Bentley to try to work
out what's going on, and I'm still mystified.  I can't see any micro
switches or position detectors that indicate the position of the sunroof.
Are these detectors in the gearbox?  Does the ECU count revolutions?  What's
going on?  Could it be another relay that's at fault?  For example, Bentley
makes reference to a Power Window/Sunroof Relay.  There's also the facility
for the remote (or holding the key in the locking position for a couple of
seconds) to close the sunroof, and then there's the delay system (power
windows and sunroof are enabled until the driver opens and closes the door
after the ignition is turned off?).

Any BTDT?  I'd be ever so grateful!

I can guess how much a new control relay would be - probably in the region
of 1/100 the value of the car!

Paul