One problem related to transmission solenoid has been reported for the 1999 Volvo S80. The most recently reported issues are listed below.
Transmission problems causing dangerous driving conditions. The transmission slips when going between 2nd and 3rd. Also had issues with the engine going to 700 rpms when going 65 mph. This is just one of the many problems. The solenoid went out in the transmission about 13000 miles ago. Currently I have three different error codes "transmission service urgent", low oil pressure stop engine ASAP", and "emission service required". I have read many other people have the same problems I have had. Nm.