Reason why the brick machine indicator does not light

What is the reason why the indicator light on the electromagnetic directional valve YV15 of the "oil motor" controlled by hot sale brick making machine made in chinae is not on? --- Possible ways to eliminate the failure of the vibration system of the brick-free brick machine: The indicator light of the input terminal X17 of the high quality qt4-15 fly ash brick machine PLC can be lit, the indicator light of the output terminal Y26 can be lit, the indicator light of the small middle relay KA23 that controls the "pre-shock" action can be lit, the output voltage on the relay circuit board is normal, The indicator light on the solenoid directional valve YV15 of the 'oil motor' does not light. Cause: The circuit between the electrical circuit board of hot sale brick making machine made in china and the solenoid valve "YV15" coil plug is disconnected or loose. Remedy: Check the line with a multimeter to eliminate the fault. Cause of the fault: The plug connection on the electromagnetic steering valve "yv15" of the high quality qt4-15 fly ash brick machine is loose or the plug is damaged.