A single output device has failed while the remainder of the PLC system is functioning normally The indicator light on the output module indicates that a signal is sent to the output point where the device is connected. You would now:

a) trace the circuit back through the logic to locate the inputs.
b) use a programming terminal to call up the rung that controls the output to see if the output coil is on.
c) check the point where the output device's field wiring is connected to the output rack.
d) check the input modules for short-circuit conditions.