Liebherr has added a second proximity sensor to its hydraulic quick coupling system.The first proximity sensor determines the position of the retracted or extended bolt. It forwards the signal whether the quick coupler is locked or unlocked to the warning buzzer or the display. The second proximity sensor monitors the position of the attachment to the quick coupler. If the bolts are extended without the attachment being connected to the quick coupler, a warning tone sounds in the cab and a warning signal appears on the display.