a coolant conductivity method and apparatus used to determine when a coolant , circulating through a vehicle &# 39 ; 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 .