Leak test, vacuum
WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
Courtesy of VOLVO CARS OF NORTH AMERICA.
Set the selector to position VACUUM.
Slowly pump out the air to minus (-) 3 kPa. Wait until the vacuum has stabilized. Pressure increases of 1 kPa per 30 seconds are permitted.
Replace any fuel filler cap that fails this test.