Update: Relayed lights. Highbeams stay on. WTH?

[Wayne Dohnal]

Here's some info that may or may not be useful.  It applies to urS4s, and I
don't know if it would apply to a later A6 or not.  On the urS4s with
daytime running lights, which happens to be those made for the Canadian
market, Audi uses the high beam power circuit to drive one side of the fog
light relay coil.  When the hibeams are on, the hibeam power wire is at 12
volts, and when they're off it's driven to ground by the hibeam filaments.
When you relay the hibeams, and the hibeams are off, the fog light relay and
hibeam relay end up being conected in series to 12 volts, and the hibeam
relay latches on.  If you suspect this could be happening to you, I believe
that pulling the fog light relay would provide a temporary fix.

Wayne Dohnal
1994 S4


>O.K. When we last saw our hero he was struggling to understand why, after
>relaying the headlights on his A6, his high beams would, once being turned
>on, not go out until all the headlights were shut off.
>
>Now after several suggestions from fans, some of them quite useful, we have
>more information.
>The high beam relay triggering voltage, formerly known as power to the high
>beams, is not measuring 0vdc when the high beams are off and low beams on.
>It is measuring 7.5 vdc with the relay removed (open circuit), and 4.2vdc
>with the relay installed (under load). When the headlights (high and low)
>are off, it measures 0vdc, with 0 ohms resistance to ground (relay
removed),
>as expected. With Headlights on, and high beams turned on, it measures
>battery voltage, ~12vdc.
>
>So; I believe that the headlight control unit (that double relay looking
>thing on the aux relay panel) is bleeding enough current to the high beam
>line to maintain the relay latched, but not enough to latch it.
>
>The question is; is it a bad controller? Or is this normal behavior for
this
>controller, which requires some type of work-around?
>
>Any thoughts gladly parsed.
>
>TIA
>Steve