[s-cars] How does it know your headlight ain't on?

[JC]

Stupid bulb check.  I think all the Audi units are roughly the same... But it's not just headlights at all, covers turns and brakes too. AFAICFO its resistance and/or current sensing. Once wiring gets wanked a little it seems hard to correct. Been told it can even happen from different brand bulbs on left vs right kind of stuff.  Or from wiring/ground deterioration on old cars. BTDT with famous hatch rewiring. Bulb check started going intermittently, which led me to find the classic hatch wire disaster. OK great i say and fix my hatch mess. However now everything on my car seems 100% fine but the "No Christmas tree ornament alert" as my wife calls it, would still light. I even tried complicated DMM checking of extensive crap including voltage at the sockets, resistance to ground at every socket, etc. Finally in exasperated irritation from having to deal with the constant BEEEEP of the thing going on/off I got pissed and neutered the bulbcheck relay. One thing I never got to try was a new relay, my bud w a C4 A6 is fine for me to steal his for a test but I always have too many beers before we get around to it and forget to actually grab it. 

So far only a useless story for you, except to try checking voltages Someone here or on QW recently had luck w replacing the relay IIRC?          

__________________________
John Cunningham

US Mobile +1 (617) 750-5025
China +86(0)136 6080 9560

Sent from iPad

On Sep 21, 2010, at 3:42, David Kase <dbkase at gmail.com> wrote:

> Patient is a B5 S4.  I get the headlight-is-out warning (I assume it is just
> detecting the headlights) but the headlight works.  The light was out and I
> found that the wire from the wheel well area into the cabin was bad.  I
> replaced the wire with a slightly different routing and the warning is still
> on.  Did I maybe bypass a component that would let the system know that
> juice is flowing to the light?  Or?
> 
> Kase
> prepping B5 S4 FS
> _______________________________________________
> S-CAR-List mailing list
> http://audifans.com/mailman/listinfo/s-car-list
> http://www.audifans.com/kb/List_information