an led drive apparatus includes a microprocessor having a configurable input / output port , a fet current control transistor , and a diagnostic interface circuit . the diagnostic interface circuit includes a transistor having an input coupled to a junction between the fet and the led , and an output coupled to an input of the fet . the microprocessor input / output port is coupled to the input of the fet for turning the led on and off and performing fault protection and diagnostics . at each desired transition of the led , the microprocessor configures its input / output port as an output and momentarily sets the output state to achieve the desired transition , then re - configures the input / output port to determine the conduction state of the diagnostic interface circuit transistor , and determines an output fault status of the drive apparatus based on the determined conduction state .