Audi A4 Alarm System Dead, No Control Unit Response

Had the same problem with my 2016 Audi A6 2.0 TFSI. The alarm system started acting up with unusual false alarms, especially during cold weather. Initially thought it was a basic power failure but diagnostic tests revealed a faulty alarm sensor in the hood latch area. The real issue was that the alarm control unit had water damage from a blocked drainage channel, causing corrosion on the circuit board. The immobilizer would sometimes activate out of nowhere, and the optical locking signals stopped working completely. Required full replacement of the alarm control module and reprogramming of the immobilizer system. Also needed to clean and reseal the drainage channels to prevent future water ingress. This was quite a serious repair as it affected multiple security systems. Worth checking your drainage points around the hood area and under the windscreen. Also, have a specialist scan for communication errors between the alarm system and the central electronics. These symptoms often point to either water damage or a failing control module rather than just battery issues.

Thanks for the detailed reply about the water damage! That drainage issue seems very similar to what I might be dealing with. After reading your experience, I am planning to have the alarm sensor and drainage channels checked first. Did you happen to remember how much the whole repair ended up costing? Also curious if youve had any other anti-theft system problems since the fix?

Glad to update, the repairs completely resolved my anti-theft alarm system issues. After clearing the drainage channels and replacing the control unit, the security alarm has worked flawlessly. The immobilizer now functions as intended and the optical locking signals with the indicators work perfectly every time. The total repair came to 45 Euro for reprogramming the alarm control to properly activate the optical locking sequence. Much less expensive than I initially feared, since no water damage was actually found in my case, it turned out to be just a programming issue with the control module. No battery issues or false alarms since the fix. The system has been reliable in all weather conditions. If your symptoms are similar, having a specialist check those drainage points is still a smart first step, even though my problem ended up being different than expected.

Thanks for the input. Finally got my issue resolved! After your suggestions, I took it to a different mechanic who specializes in security systems. Turns out the alarm control module had failed due to exactly what was mentioned, water damage from blocked drainage channels. The repair included cleaning all drainage areas, replacing the damaged control unit, and reprogramming the entire anti-theft system. Cost me 780 Euro total, but worth every cent since the false alarms have completely stopped. The security alarm now works perfectly and the battery issue with the system is resolved. Should have checked those drainage points months ago instead of wasting time with general diagnostics. Really glad I asked here, saved me from more frustration with unusual security system failures.