What happens when you press the other buttons on the wheel? Does the + button work? How about the R button?
The four buttons on the wheel are connected to the injection computer via two wires. The resistance between the wires indicates to the computer which button is pressed. The resistors are part of the wheel switch unit.
Could be a fault with the switch unit on the wheel, the wires or connectors or the injection computer itself.
Sounds to me that minus button is working like the off button.
Perhaps there is a fault with the resistor concerned with the minus button.
If the button turns the system off then there could be short circuit present.
The off button ("O") has no resistance connected to it and this is how the computer detects that the user wishes to deactivate cruise control.
I have a similar problem, when I press the + button no problem, when I press the - button sometimes it works and sometimes it doesnt when I try to press again a message "Check Cruise control" appears and the system shuts down..Donno if the system is working as it is supposed to be or it has a fault, does the cruise control system use the brakes? I mean shall I expect automatic decrease in speed when I press the - button or should I use the brakes!?