Alarm siren not sounding

[SilentBob74]

2007 VW Passat 2.0 TDI Sport estate

Had this car for about 3 years now. In all the time that I have had it there have been no chirps or indicator flashes when locking or unlocking with the remote. But the red LED on the driver's door would start flashing upon locking so I always assumed that the alarm was fine.

Already had a bluetooth OBDII dongle, but installed the Carista Android app and paid for the pro package. I can't remember why I chose to do this, but there must have been an issue that I was trying to diagnose at the time. Anyway, upon digging into all the options within the app I found that within the customisation options the alarm system was set as disabled. After enabling it I noticed different behaviour of the red LED on the driver's door. It would now flash a couple of times, then remain static for a while before then flashing again. I figured that the static stage was probably where the alarm was setting, so was happy that the alarm should now be working (not that I had realised it wasn't before). From within the customisations I also turned on both beeps and flashes for both locking and unlocking. Weirdly I still got neither. I wasn't really that bothered, so I just left it as that.

Recently (for the first time that I can think of) I managed to trigger my alarm. My wife had gone back to the car ahead of me, unlocked it and sat in it waiting without putting the remote in the dash. When I came along and opened the driver's door, all of the indicators started flashing. But there was no noise from the alarm. I have since done the same a couple of times on purpose, but always get flashing with no siren.

So doing a bit of searching and reading it becomes apparent that it is quite common for the battery sealed within the alarm siren unit to leak over the PCB board, rendering it useless. So, as many others have done, I ordered a replacement siren. I have just had this new siren fitted today and...

Still no noise when setting off the alarm. Just flashing indicators. So now I have absolutely no idea what is going on.

FYI, I have attached screenshots from the appropriate customisation page within the Carista app, where you can see that the alarm should be enabled and that the chirps and flashes should be turned on. I have also run a diagnostic which has returned some faults. These faults come back straight away after resetting them, but I'm not convinced that they would have anything to do with these alarm problems. The details of these errors from the scan log are as follows...

Body/convenience system
Part #: 3C0959433AR
Coding: 1890000841030C7F1204850D40084F2A003C80 (hex)
Component: KSG PQ46 ELV
Fault codes:
01333 Door Control Module: Rear Left (J388)
01334 Door Control Module: Rear Right (J398)

Radio
Part #: 1K0035186T
Coding: 40400 (decimal)
Component: Radio GR0
Fault codes:
01044 Control Module Incorrectly Coded

I guess that the radio error might be related to the aftermarket aux adaptor that I have got plugged into the CD changer connector on the back of the head unit. It is this Connects2 item.

I'm not sure what the problem is with the rear doors. Both lock and unlock as they should and the windows work from their own switches and from the driver's door switches. The only odd thing that I have noticed is that the interior light won't come on when the rear doors are opened.

However, if any off these were going to affect the alarm, then I would expect it to prevent the alarm arming in the first place, rather than just silencing it when it is triggered.

Can anyone help?

Thanks