Abstract: A pen fault check circuit for an ink jet printer that includes a comparator that further includes a pen signal input, and a switch array coupled to the pen signal input, where the switch array includes a high voltage diode. Also, a method of checking for faults in a pen of an ink jet printer that includes the steps of generating a pen signal from a first constant current source and a pulse line resistance from a pulse line of an ink jet nozzle, generating a reference signal from a second constant current source and an external resistance from a external resistor, where the first current source and the second current source generate equal currents, and comparing the pen signal and the reference signal to determine if the ink jet nozzle is in a fault state.