A vehicle bus system includes a controller programmed to, after issuing a command to close first and second contactors, wherein the first and second contactors are arranged to share a first terminal of a battery, the first contactor is configured to power a first load when closed, and the second contactor is configured to power a second load when closed, initiate pre-charge of a second terminal of the battery in response to respective first and second voltages across the first and second contactors exceeding corresponding first and second closed-state voltage thresholds, and generate a notification and preclude initiation of the pre-charge in response to one of the first and second voltages being less than the corresponding first and second closed-state voltage thresholds.