VW Up Alarm Failure: Siren Communication Error Fix

Had the same alarm system fault on my Polo 1.0 TSI from 2017. The vehicle security issue was traced to corroded wiring connections at the siren module under the right front wheel well. Water ingress had damaged the plug connecting the siren to the main alarm control unit. This is a known weak point, the siren mounting location makes it susceptible to water and road debris. A proper fix requires removing the wheel well liner, replacing the damaged connector, and adding additional waterproofing. The alarm reset after repair was straightforward but needed proper diagnostic equipment to clear the fault codes. Would not recommend attempting this as a DIY job since accessing the components requires partial disassembly of the front end, and the alarm disarm procedure needs dealer-level tools to properly reintegrate the siren with the security system. The repair itself is not particularly complex for an experienced technician, but proper diagnosis is crucial since similar symptoms can also point to a failed siren unit or main control module. A dealership visit is advisable to avoid trial-and-error parts replacement.

Thanks for your detailed response about the alarm controller issue. Mine turned out to be very similar, water damage to the signal connection under the wheel well. The mechanic found it pretty quickly once they knew where to look. Did the repair hold up well since then? Interested to know if you had any recurring alarm system problems. Also, would be helpful to know roughly what the fix cost you, trying to figure out if my quote is reasonable since these vehicle security repairs seem to vary quite a bit in price. My Up has been back on the road for a few days now and everything seems stable, but planning to keep an eye on it, especially after heavy rain.

Good to hear you got it sorted out with your Up. After my repair it has been working flawlessly for over a year now, even during the wettest months. No more signal problems or fault detection warnings with the automotive alarm. The fix cost me 95€ for replacing the damaged cable connection and applying extra waterproofing to prevent future corrosion. This seems to be the standard rate for this type of alarm system repair when the issue is just the connector. Your quote sounds about right if they did similar work. The key was getting the exact diagnosis right away instead of replacing the entire alarm controller or siren unit unnecessarily. Since having the connection properly sealed, the siren communication has been reliable and the alarm disarm function works perfectly every time. Just keep monitoring after heavy rain as you mentioned, but with proper waterproofing applied during repair, you likely wont see this issue again. The fix is generally permanent as long as the new seal remains intact.

Appreciate all the feedback from everyone. After getting my Up back from the mechanic yesterday, I can confirm they found and fixed the same issue. The security breach was indeed caused by water damage to the wiring, just as suggested. The repair cost me 110€, which included replacing the corroded connector and adding extra waterproofing to prevent future issues. The mechanic was able to diagnose the automotive alarm problem quickly once they knew where to check, saving time on unnecessary parts replacement. They showed me the damaged area under the wheel well, pretty obvious once you see it. The signal problem was clear from the corrosion on the old connector. After cleaning everything up and installing the new parts, they ran a full system check to ensure the alarm controller was communicating properly with all components. Really glad I didn't attempt this as a DIY job. The location of the siren made access tricky, and resetting the vehicle security system needed special diagnostic equipment. So far everything is working perfectly, fingers crossed it stays that way through the rainy season.