Hi Marek
Cars equipped with VolvoOnCall (VOC) have a backup battery in the PHM
In fact, the PHM also has a backup microphone and speaker and GSM antenna.
Reason:
- In the event of an accident where the vehicle's battery is disconnected, the PHM backup battery has sufficient battery power to make an emergency call or a number of calls
- In the event of an accident where the vehicle's microphone is disconnected or damaged, the PHM has an internal microphone and thus voice calls are still possible
- In the event of an accident where the vehicle's audio system is disconnected or damaged, the PHM has an internal loudspeaker and thus voice calls are still possible
- In the event of an accident where the vehicle's GSM antenna system is disconnected or damaged, the PHM has an internal GSM antenna and thus voice calls are still possible
There is quite a bit of well thought out redundancy in the OnCall system
The PHM, once triggered, becomes a standalone module that can make emergency voice calls even when the rest of the vehicle has been demolished around the PHM
If your system will not support OnCall, then you should make your buyers clearly aware of the fact that the OnCall system will become non functional when your replacement BT-PHM is fitted.
Especially as some people consider the Volvo OnCall as a life saving insurance policy if they have an accident!
In reality, the users who will thus deliberately disable their OnCall system should fit a sticker to the OnCall button stating that OnCall is not functional.
And insert a page in their vehicle documentation stating that it is non functional for other drivers or future owners to be aware of.
Given the highly integrated nature of the Volvo OnCall functions - integrated with CAN bus, SRS system, GPS system, etc, I would be very cautious about disabling the VOC system, as it is regarded by the manufacturer as a vital vehicle safety system.