A coolant conductivity method and apparatus used to determine when a coolant, circulating through a vehicle's coolant system, starts to conduct electrical current and loses its electrical isolation properties. The system includes a battery monitor controller senses one or more isolation resistances placed throughout a fuel cell system and is programmed to run an isolation algorithm. The isolation algorithm opens and closes contactors in a specific order, measures the resistance of the one or more isolation resistances and calculates a coolant conductivity value. The system will indicate when the coolant needs to be replaced.