Cadillac XTS Alarm System Failure Troubleshooting Guide

I had a similar issue with my 2017 Cadillac CT6. As someone with some experience working on car electronics, I first suspected a power failure affecting the security alarm system. The symptoms matched yours exactly, no alarm activation and the immobilizer giving trouble. After running diagnostics, it turned out the alarm sensor needed recoding. The alarm control unit was working fine, but the programming had somehow reset, preventing proper communication with the central locking system. The fix was straightforward, the workshop reprogrammed the alarm system to properly activate with the optical locking signals. Total cost was 45€ for the programming service. No parts needed replacement, which was fortunate. To better assist with your situation, could you share: Have you noticed any battery issues recently? Does the key fob work normally for locking/unlocking? Are there any other electrical systems showing unusual behavior? Did this start suddenly or gradually? This could help determine if its just a programming issue like mine or if theres a deeper electrical problem to address.

Thanks for sharing that information. With my XTS having similar symptoms now at 104480 KM, I was initially concerned it might be the entire alarm control module. After reading your experience, I checked the key fob battery which was actually quite weak. However, replacing it didnt solve the anti-theft system errors. The immobilizer seems to engage properly but the alarm sensor stays inactive. No issues with any other electrical components. Getting slightly worried the repair might cost more than just a reprogramming job, but good to know yours was resolved without replacing parts. Booked a service appointment next week to have them investigate. Based on your post, I will ask them to specifically check the sensor programming before suggesting any parts replacement. Hope its just a similar coding issue.

Thanks for the update on your XTS situation. Interesting that the key fob battery replacement didnt resolve the false alarm issues. From my experience with the CT6, even after finding the programming solution, we discovered the alarm sensor wiring harness played a role in the intermittent security alarm failures. While my initial fix was just programming, about 2 months later the anti-theft system started acting up again. The technician found slight corrosion on the alarm sensor connections causing signal interruptions. A thorough cleaning and protective coating of the connections fully resolved the issue. Total cost for this second fix was 85€ including labor. Since your mileage is similar to what mine was when the issues started, definitely have them inspect the wiring and connections. The programming might solve it initially, but checking these physical components could prevent a repeat visit. Keep us posted on what the service finds. The alarm control module itself is usually quite robust, so hopefully its just the sensor connections or programming like in my case.

Thanks for all the insights about the alarm system problems. Just got back from the service appointment for my XTS, and it turns out you were spot on about checking the connections. The technician found corrosion on both the alarm sensor and immobilizer wiring, which explained why the anti-theft system was acting up. The total repair came to 160€, they cleaned all connections, applied protective coating, and also reprogrammed the alarm control unit since they found some stored error codes. More expensive than just the programming fix, but still better than replacing the entire module. The car alarm now activates properly when locking, and the immobilizer works as it should. Really glad I asked about this before going in, as it helped me discuss the issue more knowledgeably with the service team. They mentioned these connection problems are somewhat common at higher mileage, so regular inspection of the wiring might prevent future issues. Will monitor the system over the next few weeks to ensure everything stays working correctly.