Error Code 4: No signal from the hook up reed switch

First check the position of the reed switch at top of the hook up cylinder. The light should come on 2mm before the end of the cylinder stroke. In order to check this though the light does need to come on therefore check the wiring at the circuit board plug. If the reed switch is working and in the correct position then check the free movement of the hook mechanism, the air supply and the relevant pneumatic valve.