step 408 in an actuator circuit that has failed as an open circuit applying a continuous current to the failed circuit could cause a voltage to build up across the two branches of the open circuit where the test signal used in step 408 is a continuous current in step 410 the vcc 210 b may use a test signal such as a pulsed current this can allow voltage built up during the pulsed current to dissipate during periods when the diagnostic current is off in some embodiments some or all of the vccs 110 a and 110 b the kernel boards 224 a and 224 b and the application boards 246 a and 246 b may be implemented using a processing device and a memory that includes program code in other embodiments some or all of the vccs 110 a and 110 b the kernel boards 224 a and 224 b and the application boards 246 a and 246 b may be implemented with fixed or programmable logic configured to perform the methods described above kernel board 224 a and application board 246 a and similarly kernel board 224 b and application board 246 b may be implemented as single printed circuit board pcb or as two separate pcbs in some embodiments various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium the phrase u201c computer readable.