In an example, a vehicle diagnostic system is disclosed. The vehicle diagnostic system includes a first DC-DC converter having an input and an output and a second DC-DC converter having an input and an output. The output of the first DC-DC converter is connected to the input of the second DC-DC converter at a first node, and the output of the second DC-DC converter is connected to the input of the first DC-DC converter at a second node. The vehicle diagnostic system includes a battery connected to a vehicle load and the first node and a redundant power source connected to the second node. The vehicle diagnostic system includes a control module that is configured to initiate operation of the first DC-DC converter and the second DC-DC converter to cause current re-circulation between the first DC-DC converter and the second DC-DC converter.