One problem related to power door locks not working has been reported for the 2006 Volvo S40. The most recently reported issues are listed below.
After a long period of rain, water pooled on rear driver and passenger floor. Windows would not function, door locks would not function, turn signals didn't work. Instrument panel flashed warnings of engine problems, brake failure, airbag problems. Often lost entire panel while vehicle was being driven on highway, measurements going dead. This has been going on for months and is getting worse.