open wire detection of open drain output
Try this: -

It uses a window comparator and, under normal operation the voltage into the window comparator is \$\frac{2.2}{3.2}\times V_{CC}\$ and, when the MOSFET operates that voltage gets close to 0 volts but, importantly, if the wire link is broken, the voltage sensed by the window comparator is close to \$V_{CC}\$ thus indicating a wire open fault: -


INPUT is the voltage level on the wire
VrefHi for a Vcc of 5 volts would be about 3.5 to 4 volts
VrefLo for a Vcc of 5 volts would be about 2 to 3 volts

You can mount the 2K2 resistor on the output terminal block of the motor controller module in parallel with the wiring that goes to your PCB.