We have a B39 2007 and since new have had a problem with the ignition switching itself on immediately after being switched off. It usually switches off and remains off the second time. It does not occur every time on switch off but about 80% of the time. No one seems to know what the problem is. Any ideas?
Do you mean that the engine continues to run or is this just the instruments? If the engine runs again how long are you holding the switch in the 'off' position?
My first thought is that there may be water/corrosion in the switch. These are not expensive to replace (if you don't go to Volvo that is ;) ).
Sounds like you have a dodgy switch.
You can get replacments from Keypart