Brake lamp switch
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 engine control module (ECM) transmits a signal on the Control area network (CAN) indicating whether the brake lamp switch is activated or not. The gearbox control module (TCM) uses the signal for the internal gear functions and diagnosing the gearbox.
OFF = Brake lamp switch unaffected
ON = Brake lamp switch affected