2005 Volvo S40 with about 100k kms. Every once in a while, usually after I've just parked the car, exited, and locked it, the alarm will go off.
I understand there is a common issue with these vehicles. The siren module has a backup battery, so the alarm can sound even if the main battery is disconnected. I've pulled the module out and cut it open, expecting to find an old, dead, leaky battery that's destroyed the circuit board inside. It turned out to be in great shape.
While I had the siren module out, I've continued to drive the car. I've noticed after parking that the alarm continues to be triggered. While there is no sound with the siren out, the lights flash and I get a notification on the dash the next time I get in that the alarm was triggered. This doesn't happen every time, only occasionally. This suggests to me the siren module is unrelated.
I tried a second test where I put the alarm into a "reduced" mode with a button on the ceiling. This disables the motion detection for when animals are left in the car, or on ferry crossings. I've noticed at least once where the alarm was still triggered, which suggests the motion detection component is also unrelated.
I'm now thinking this has something to do with the door, hood, or trunk sensors. I've armed the car and walked around trying to wiggle the doors, hood, and trunk to see if I could cause the alarm to sound, without result.
Does anyone have an tricks or suggestions to track down the source of the alarm triggering? Is it possible to get any information about this problem using a standard OBDII scan, or do I need to use the VIDA tool?