Re: Central locking

[ti@bazooka.amb.org (Ti Kan)]

Alasdair Mackintosh writes:
>   I have a early 1986 model Audi 80 ( Audi 4000 in the US, I believe) whose
>   central locking recently died on me. The pump that drives the system is
>   still fine - I connected the battery to its terminals, and the locks opened 
>   and closed. This suggests, even to inept electricians like me, that there's
>   something wrong with the wiring. (It isn't the fuse. Life ain't that simple.)
> 
>   Before I start to trace through all the wiring, I was wondering if anyone else 
>   has had a similar problem, and could give me some clues as to where I should 
>   start looking.

The Audi central locking system is actually extremely simple as far as
electrical wiring is concerned.  The only wiring is to the driver's
door and to the pump itself.  There is no wiring to the other doors,
only air tubes.  The driver's door has a plunger-type switch that
detects whether you are locking or unlocking the door (it is a
single-pole double-throw design).  The central contact of the switch
is wired to a fused 12V line on the fuse relay panel, and the two other
contacts to the central locking pump.  The pump itself has three
electrical connections, two of them from the aforementioned door
switch, and one to ground (tied to the body in the luggage compartment).
That's all!

Before you dig into the wiring, verify that the fuse is not blown.
On U.S. 1986 4000 models, this is fuse #19 (10 Amp) on the fuse-relay
panel.  If the fuse is good, then use a voltmeter to measure the
terminal 1 and terminal 3 on the central locking pump.  You should have
12 volts on one of them with the driver's door in the locked position,
and 12 volts on the other when the door is unlocked.  If you only get
12 volts on one of them but not the other as you lock/unlock the door,
then the culprit can be either the wire from the plunger switch to the
pump, or the switch itself.  If you don't get 12 volts on both lines
then the problem is likely to be either the switch or the 12 volt line
from the switch to the fuse/relay panel.  Carefully remove the inside
door panel and remove the switch and test it with a continuity tester.
If the switch is good, then the wiring is bad.  Are you getting 12 volts
on the line (typically a red/black wire) at the switch contact #2?

Good luck...

-Ti
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