Central Electronic Module (CEM) (2005-2006): Function: Horn
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.
The horn is operated when the steering wheel module (SWM) (3/254) receives a signal from the switches (3/37) in the steering wheel. The steering wheel module (SWM) sends data to the central electronic module (CEM) (4/56) via serial communication indicating that the switch is closed. The central electronic module (CEM) activates the relay for power supply to the horn.
There is also a signal directly connected from the steering wheel module (SWM) to the central electronic module (CEM). This is a Limp-Home function.