A diagnostic system for a voltage regulator is provided. The diagnostic system includes a microcontroller having first and second analog-to-digital converters and first and second output ports. The first analog-to-digital converter outputs a first voltage value corresponding to the first voltage from the voltage regulator. The microcontroller executes a first diagnostic function to set a first voltage regulator diagnostic flag equal to a fault value indicating a voltage out of range condition, if the first voltage value is greater than a first threshold voltage value or the first voltage value is less than a second threshold voltage value. The microcontroller executes a second diagnostic function to stop generating first and second control signals to de-energize a contactor coil to open a contact of a contactor if the first voltage regulator diagnostic flag is equal to the fault value.