Cadillac CTS Alarm Failure Linked to Auxiliary Battery

Had a similar issue with my 2008 Cadillac STS. The auxiliary battery failure caused the car alarm system to act unreliably before stopping completely. A proper battery check revealed two separate issues: the main car battery was fine, but the smaller auxiliary battery that powers the alarm system had degraded. This is a common problem in Cadillacs of this era after about 8-10 years of use. The fix required replacing the auxiliary battery unit and recalibrating the alarm system. The symptoms match your situation, error messages and complete alarm failure are typical signs of auxiliary battery degradation rather than a main battery issue. This was not a major repair in terms of complexity, but it needed immediate attention since a failed auxiliary battery can eventually drain the main battery and cause starting problems. The alarm system serves as a key security feature, so operating without it working properly is not recommended. Worth noting that the battery issues can sometimes mask other electrical problems. Having both batteries tested and the charging system verified would be a sensible approach before proceeding with repairs.

Thanks for sharing your experience with the auxiliary battery and alarm system problems. Sounds very similar to my situation. Just got it fixed last week actually. The electrical issue symptoms matched exactly what you described, complete alarm failure followed by those annoying error messages. In my case, the battery check confirmed it was definitely the auxiliary battery causing problems. Just wondering, do you remember roughly how much the repair cost you? Also, has everything been working properly since the fix, or have you noticed any other electrical problems popping up? My Cadillac CTS is running fine now, but always good to know what to watch out for with these car battery systems.

Getting my STS's battery problem fixed cost around 330€, which covered both diagnosing the electrical issue and replacing the aging auxiliary battery. Since the repair, the car alarm system has worked flawlessly, no more battery alarms or system errors. The car battery warning lights and electrical system warnings have completely cleared up. The auxiliary battery replacement solved all the alarm-related issues, and I have not experienced any additional problems in the months since. Most importantly, the Additional battery alarm system defective message that kept appearing on the dash is now gone. Having a properly functioning security system again gives real peace of mind. If your CTS starts showing any new electrical issues, address them quickly. But from my experience, once the auxiliary battery is replaced and properly calibrated, these car alarm problems tend to stay resolved.

Thanks for all the advice everyone. I wanted to close out this thread by sharing my experience getting the repair done. Took the car in last Thursday for a system diagnosis. The mechanic confirmed the auxiliary battery problem through a detailed battery check. Total repair came to 295€, which included parts and labor. They had to order the specific auxiliary battery unit since they did not stock it. The electrical issue turned out to be exactly as described, the old auxiliary battery had degraded and was causing the car alarm failures. Whole repair took about 2 hours once they had the part. The car alarm now works perfectly and all those annoying error messages are gone. Really glad I got this fixed rather than trying temporary solutions. The mechanic mentioned these failing auxiliary batteries often cause bigger electrical problems if left unchecked. For anyone else facing similar symptoms, definitely worth getting a proper battery check done early.