When independent mechanic Joe Marconi replaced a faulty windshield-wiper switch last summer on a 2004 Saab—a minor type of repair often done at his shop—the car wouldn't start.

Mr. Marconi, who owns Osceola Garage in Baldwin Place, N.Y., discovered the switch needed to be "initialized," something only a Saab dealership can do. Initializing is a problem that has been happening more and more often, says the 55-year-old mechanic.

"The...