Para simular la pulsación de una tecla del volante tienes que enviar un mensaje por el CAN Bus Confort o por el infotaiment. Se replica el mensaje en los dos.
El ID del teclado del volante Audi es el 5C3h
#define AUDI_MULTI_RUL 0x5C3
/*
5C3 2 39 00 none
5C3 2 39 02 Prev
5C3 2 39 03 Next
5C3 2 39 04 Scan Up
5C3 2 39 05 Scan down
5C3 2 39 06 Volume+
5C3 2 39 07 Volume-
5C3 2 3C 2A Phone button pressed
5C3 2 3C 00 Phone button released, changes to 39 00 after a second or so
5C3 2 3A 1C Mode button pressed
5C3 2 3A 00 Mode button released, changes to 39 00 after a second or so
5C3 2 39 01 Mode button pressed before it turns back to 39 00
5C3 2 3A 1A up/down button pressed within 2 seconds after pressing Mode button
5C3 2 3A 02 up within 2 seconds after pressing Mode
5C3 2 3A 03 down within 2 seconds after pressing Mode
5C3 2 3B A7 vol up/down pressed
5C3 2 3C 07 vol down after pressing phone button
5C3 2 3C 06 vol up after pressing phone button
*/
Fuente: http://audiforum.us/threads/id-codes-can-protocol.4999/