When i shut off the engine on my 2005 volvo s40 t5, a small electric motor continues humming and clicking for about 1 minute.

SOURCE: 2005 volvo s40 t5 how to reset oil light

turn the key on to position 1 preset miliage trip button anh hold for 2 second release and turn key to position 2 hold within 4 secods and hold til manitance info clears.

SOURCE: 2005 Volvo S40 won't start

sounds like an immobilizer issue you have to take it to dealer

SOURCE: 2001 Volvo V70-T5 fuel guage malfunction

I had a similar issue and started to notice other electrical failures along with the gas gauge. My rear doors would not lock and my rear wiper stopped working. I started pulling fuses and relays to see if this would reset, no go. But then I hit the jackjpot. In the rear electrical panel, below all the fuses and relays is a 2" x 2" black plastic square with a big screw in it.

Remove the screw and pull evenly on the black square. This seems to be a major electrical hub for the car. I reconnected and all 3 of my issues disappeared...I read somewhere that a fix might be to disconnect the battery for a few minutes, which I guess re-sets some relays and circuits, but I guess this did the same thing. Good luck.

SOURCE: 2005 Volvo S40 T5 is losing power while driving

had this problem as well.. check the oxygen sensor on it (sometimes critters like that wire) or like shel said dirty injectors or filters could be it.. bad gas is also another one... dont go to places with old tanks or that is really cheap, run at least 91

SOURCE: my volvo s40 t5 2005 is suddenly losing power as

if computers arent picking anything up its not an electrical fault, sounds like your surging because of bad fuel or blocked injectors, run some fuel cleaner through the car and see if that makes a difference. fuel filters may need to be changed but try the cleaner first.