This is a lovely car, though this fault took it off the road for 4 days. This car is the B5 mild hybrid version. It has about 12000km on it. Here's what happened:

• In retrospect, the TCAM (communications modem) had probably been faulty from new, with the network connection on the infotainment system occasionally dropping out for a few hours, then coming back.
• I came back from a week away to find the car completely dead. No response to key, and when I opened with the metal key in the fob: no beep, no lights, no displays - nothing. Dead. (I had previously not used the car for up to 2.5 weeks without problems,)
• Called Volvo Assist, got a jump start
• Then seemingly all good except there was a blinking red light on the SOS call button, and a warning light on the main instrument display about the SOS system. The blinking red went to steady red when I pushed the button briefly.
• The car drove normally, and after about 10 minutes the start-stop system started working. There was clearly enough charge in the 48V system to restart the engine at that point. I drove for another half hour for good measure..
• Parked the car and twisted the start-stop **** to turn off. At this point all the electrics suddenly died again - couldn't even lock the car.
• Called Volvo Assist the next morning, got a jump start, drove to the dealer.

This is what the dealer found and did:

• 48V system was at 2.6V, 0% charge and 12 V battery at 7% charge
• Took the batteries out, charged them for 24h, put them back in, upgraded all software, and found 0.3A standby load (I think on the 12V system) which is in spec
• 48V battery went from 88% to 69% after 25 minutes of standby, so they decided it was faulty and replaced it
• After that, the TCAM faults were still there so they did a hard TCAM reset (it looks like they basically did this) then a TCAM software upgrade
• TCAM was still dead so they replaced it

And now the car's working fine again.

What I think happened was that the TCAM failed and drained the batteries completely, maybe just from the bright blinking red SOS light over a week. An out-of-spec 48V battery didn't help the situation.

There's a summary here of issues with the TCAM in Polestars, which use the same module:


So here's the lessons:

• Network problems with the car indicate a dodgy TCAM. If it goes, it can take the whole car down. It's probably a good idea to pester a dealer to fix TCAM problems before they disable the car.
• Jump starting the car may be surprisingly necessary. Turns out these things are quite cheap and I bought one:

 

My Volvo V60 mild hybrid is 8 months old. The onboard screen went black with a blue line to reboot the computer.... It failed again. I drove it to a Volvo garage and they downloaded software. Drove it 500 yards away from the garage and it crashed again.... Got home parked but when I tried to open the car again it had locked me out. The malfunctioning computer had drained the battery. Volvo Assist sent out a flatbed which is to deliver my car to the Volvo garage ..... So I am left with no car.... and no idea when I will get mine back. I have also lost faith in it as I am left wondering whether this will happen again when I am in the back of beyonds such as Mull or the Pyrenees .... I have always had Volvos and I thought an upgrade to a Mild Hybrid would be a good thing... Not so sure now.