WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Additional Heater And Parking Heater 912
Courtesy of VOLVO CARS OF NORTH AMERICA.
This diagnostic trouble code (DTC) means that the control module in the factory registered a fault when the heater was started but that the fault is no longer present.