Good evening all,

I have a 2004 W220 with 180,000 mile. Recently my neighbors mentioned that in the middle of the night my alarm system has been going off. The horn blowing, lights flashing inside and outside of the car. Each time there isn't anyone near the vehicle. Any suggestions of where to start? Is it possible to reset the alarm system?

I'd also like to know the location of the auxiliary battery? Would a weak auxiliary battery cause the alarm system to go off intermittently?

Thank you for your reply.

Ron

__________________

This issue occurs on the W210 chassis which was developed in the same era and uses many of the same components. It is caused by the alarm siren. The siren has an internal battery that dies. It isn't user replaceable.

I don't know if the W220 has an auxiliary battery.