I recently bought a 2010 Volvo S40 (non-turbo) with 130k miles on it. I bought it from a private seller and noticed that the trunk release button on the key fob did not function. However, the trunk release button above the license plate worked normally.
About a week ago, the trunk release button stopped working as well. The only way into the trunk is through the back seat to pull the manual release cable.

There are three wires on the button on the trunk.

1 -- 2 --
3 --

There is 12 volts across 1 and 2 and 2 and 3. When you push the trunk button, the voltage across 2 and 3 drops to 0 volts. I've read that there is a problem with the wiring harnesses, but that doesn't seem to make a difference and I can find no chaffing on the harness. I am thinking that there may be two problems: 1 the key fob (the rest of the functions on the fob work.) and 2 the trunk release button.

Any suggestions on what to look at next? Thanks!

 

btw, how the heck do you get the carpet off the interior of the trunk lid?? It's hung up on the small recessed handle and I can't see a screw or anything holding it.