On a 2001 Audi A4 Avant quattro 1.8T:

When I first bought the car in April 2012, it used to "beep" its alarm horn and flash the corner lights once when I locked it using the remote. Over the last few months, that "beep" and corner light "flash" have disappeared. However the corner lights do blink (twice) when I unlock the car.

If I hit the "panic" button on my remote all corner lights flash and the alarm horn sounds repeatedly. I can clearly hear the sound coming from the rear left quarter panel. So I know the alarm horn works fine. I can trigger the alarm purposely in multiple ways, and the alarm horn sounds just like it should.

I've located the alarm horn on the left side, behind the CD changer, and it appears to be a standard metal horn, not a battery-backup horn sounder.

I've also confirmed that the V94 central locking module is in excellent shape and has not seen any water. There's no signs of water intrusion anywhere inside the car.

I've tried changing the coding on the central locking module using VCDS, but the +00512 and +01024 options seem to do nothing. Every other coding option works fine except those two. +00512 is Remote Control "Close" Confirmation (1x Blink). +01024 is Confirmation Anti-Theft Warning System Horn Activation. Both were enabled on my car from the factory. Enabling and disabling them doesn't appear to affect anything anymore. The module accepts the coding, but the horn still doesn't beep and the corners lights still don't flash when I lock the car using the remote.

I used VCDS to go through output tests on the central locking module. One of the output tests is to check for the anti-theft arming confirmation beep. It appears to work fine, the alarm horn beeps briefly when performing that test.

I've tried re-matching all our keys to the car using the instructions in the service manual and that worked fine, but it did not bring back the horn beep or corner light flash when I lock the doors. All batteries in our key fobs appear to be healthy (at least 3v from every battery).

I'm at a loss. I'd really like the confirmation beep (and flash) to come back. I have no clue why it disappeared in the first place. Near as I can figure, everything works fine. But for some reason, the corner lights and horn are not being triggered when I lock the car using the remote.

 

Even though I only just started this thread, I've actually been diagnosing it for at least a month now. It's ironic that when I finally go ahead and post the question on a forum, I end up finding the solution the very same day.

After some more diagnosing with VCDS, I noticed something a bit odd: the car thought the hood was always open. Apparently the switch that detects an open hood is defective. So while the doors were locking and the anti-theft system was arming, not all doors were registered as "closed", so the central locking mechanism did not trigger the horn or the corner lights that mean the car is "secured". The fix was pretty simple... unplug the hood sensor. It's a normally-open switch that only closes when the hood is open. So if I unplug it (at the bunch of connectors next to the power steering fluid bottle), then it registers as "always open" and the system thinks the hood is closed.

Voila, problem solved. Now the horn beeps and the corner lights flash when I lock the doors with the remote.

I may or may not buy a new hood switch to replace the faulty one. It IS a functional part of the anti-theft system, but it's also just another part that can fail... there's more than enough of those parts on Audis as it is.

 

I've a 2001 Audi A6 2.7t. When I lock or unlock the beep sound is too low and I can unlock or lock it when I go close to the car only. Lock/unlock system is not working more than about 15 feet distance. Please help what could be the reason.

 

Yikes, start your own thread regarding this. Otherwise no-one will ever answer you in this dead one.

Also, this is the B5 forum, not C5.