A diagnostic system for a DC-DC voltage converter is provided. The DC-DC voltage converter has a high voltage bi-directional MOSFET switch. The high voltage bi-directional MOSFET switch has a first node and a second node. The microcontroller samples a first voltage at the first node at a first sampling rate utilizing a first common channel in a first bank of channels to obtain a first predetermined number of voltage samples. The microcontroller determines a first number of voltage samples in the first predetermined number of voltage samples in which the first voltage is less than a first threshold voltage. The microcontroller sets a first voltage diagnostic flag equal to a first fault value if the first number of voltage samples is greater than a first threshold number of voltage samples indicating a voltage out of range low fault condition for the analog-to-digital converter.