Audi A6 C6 2.0tdi avant - remove alarm siren

[Moses009]

Hi, because I couldn’t find any pictures or accurate info, here’s where to find the alarm horn or siren. My car is a 2007 and I have a very annoying slow parasitic drain which I haven’t been able to solve. I am a competent mechanic and have done plenty testing as per loads of online guidance to trace it but no result. Anyway the alarm siren can be a problem for draining the battery sometimes, so cause the car is old and tatty I just removed it and disconnected it. The pictures show where it is located. Hard to get out but it’s do-able with the computer cover removed. One 10mm bolt holds it in beside the bonnet hinge and just have to forcefully wiggle and squeeze it out over the edge of the computer housing. Unplug the siren and tape over the plug. I tucked mine under the wing lip so it wouldn’t get water on it. 
- remove bulkhead plastic tray covering brake reservoir etc 
- remove two torx screws located in centre holding windscreen wiper motor plastic cover. Pull cover out of lip at bottom of window above the computer on passenger side only so you can bend it up to get hands under it.

- remove 5 torx screws holding computer cover. One is hidden on left side but you can feel it. Pull cover towards front and comes of easy. 
- remove 10mm bolt holding siren and remove. Circled red in photo.

[cliffcoggin]

How can you be sure there is a drain on the battery? Have you measured it with an ammeter?

Edited Thursday at 11:42 PM by cliffcoggin
Spelling error

[Moses009]

Yup- goes down to virtually zero drain through ammeter after 10mins after locking the car. Battery is new and tested good just in case a bad one. Alternator is new even tho old one was working well. Replaced it just due to original at having done 160k. Got icarsoft diagnostic for checking for any faults too. Battery module in wheel well beside battery is good too. As I said just removing siren on off-chance because some forums say it can cause a parasitic drain. Something is possibly switching on again after car is shut down, but no idea what. Not bothered in slightest about siren not working. Car is worth peanuts and it’s not a thief magnet for sure!

[cliffcoggin]

Something does not ring true about this storey. If we assume a fully charged 60 ampere-hour battery and it is flat in ten minutes it must be discharging at 360 amps! That is twice the load a starter motor imposes, and is enough to melt any cable and cook the battery. So I ask again, what current did you measure with the ammeter?

[Moses009]

I said the ammeter goes down to virtually zero drain in 10 mins! Not the battery drains in 10 mins. The battery goes down to about 11.6 volts if car is left for 2-3 days. It’s not completely consistent either. Sometimes after 2-3 days there’s 11.8 - 12v in battery. Been like this for about 6 months. It starts on 11.6 just if not too cold outside although leave it more days it goes lower and needs jumped. Anyway the point of the post is showing where the alarm siren was located which might help someone. 

[cliffcoggin]

I was not asking about voltage, though your voltage readings suggest the battery is defective, I was asking about current, i.e. the number of amps draining out of the battery. For that you need an ammeter not a voltmeter, though most people use a multimeter which can measure both properties amongst others.

FYI The current in amps is a measure of how much power is being drawn from the battery. The normal drain is less than 0.1 amps, which is the backgound consumption for things like the alarm system and the door lock receiver.

[Moses009]

😁 This is getting quite amusing. (My repeat reply btw is a mistake due to a clumsy thumb.) Anyway I think an independent adjudicator would agree that although my reply may not be absolutely without criticism, I did clearly say I was using an ammeter. It was a multimeter as an ammeter. Connected through the battery earth to the body of car. And yes it did go down to actually below 0.1 amps after 10mins. Locked the car with multimeter connected as above and screen clearly showing in the boot. Did it more than once to check.  Plus I did say my battery was good. Charged it up independent of the car and holds its charge above 12v if not connected back to the car. Plus I used a good battery from another car, which also drained to below 11.6 volts after 2-3 days or so. Plus my alternator charges 13.8 volts at the alternator and on the battery terminals when car is running. 
JTLYK ( just tae let ye ken) I do all my mechanical work, bodywork and electrical work on my own cars and my car never sees a garage apart from Mot time. Have done for 40 years. 
If I can’t resolve this one- which I’m not over anxious about tbh - I may call in an auto electrician with some more sophisticated gear, or who may have experience of likely causes and that will be a first for me - paying someone else to fix a problem on one of my cars. I’ve read everything I could get find on every forum and nothing definitive or obvious causing the problem- plus as I said the ammeter shoes there shouldn’t be a problem. Something is switching back on I think and drawing current. I’d need more sophisticated gear perhaps connected with a Bluetooth connection to my phone with software recording draw over 12 hours or so- something like that anyway. 

[cliffcoggin]

Well having now sorted our volts from our amps, and are talking the same language, let's see if we can get a little closer to the problem.

The normal background drain from a battery is typically about 50 milliamps. If yours is losing significantly more than that, then some electrical circuit is still in operation. Removing each fuse in turn and measuring the current flow across the contacts with your meter should reveal what is still live, though be aware that some multimeters will be damaged by high currents.

On the other hand if the only loss from the battery is a few dozen milliamps yet it still goes flat then the battery has an internal fault and must be replaced. It doesn't matter if it still starts the engine, it doesn't matter if it is still showing 12.4 volts, it is clapped out. Many owners, and I was one once, refuse to accept that a battery can be defective and still start the engine, but it's true. The nature of modern car electronics is a need for a stable power supply not just a minimum voltage. In fact I suspect the "parasitic drain" I see mentioned from time to time in the forum is more likely a weak battery most of the time.

Anyway, if and when you fit a new battery you will need to have it coded to the car. See this for an explanation of how and why. Blithely swapping batteries around as we both did forty years ago is no longer feasible.

https://www.youtube.com/watch?v=5ysatH73_gM

PS. I have hidden your earlier duplicate reply for neatness. Let me know if you want it exposed again.

Edited 18 hours ago by cliffcoggin
omission