Central Electronic Module (CEM) (2005-2014): Function: Horn
WARNING: This page does not describe the selected car, but rather 12 other vehicles, including the 2014 Volvo XC90, 2013 Volvo XC90, 2012 Volvo XC90, 2011 Volvo XC90, and 2010 Volvo XC90. 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.