2003 Volvo XC70FACTORY OEM SERVICE PROCEDURE

Central Electronic Module (CEM) (2001-2004): Function: Horn

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2007 Volvo V70, 2006 Volvo V70, 2005 Volvo V70, 2004 Volvo V70, and 2003 Volvo V70. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Horn Input And Output Signals
GLL106029Courtesy of VOLVO CARS OF NORTH AMERICA.

The horn is operated when the steering wheel module (SWM) (3/130) 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 the control area network (CAN) indicating that the switch is closed. The central electronic module (CEM) activates the relay (2/17) 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 used if there is a fault in the control area network (CAN). This is a Limp-Home function.

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