Fault diagnosing system and method for coolant switching device for vehicle

A fault diagnosing system for a coolant switching device for a vehicle, comprising:

• a first coolant pipe line that passes through an electronic device and a heating device;
• a second coolant pipe line that branches off the first coolant pipe line at a first end thereof, a middle portion of the second coolant pipe line extending to pass through a radiator, a second end of the second coolant pipe line joined with the first coolant pipe line;
• a coolant switching device disposed at a branching point at which the second coolant pipe line branches off the first coolant pipe line;
• an on-board charger configured to charge a vehicle battery and disposed on the second coolant pipe line between the coolant switching device and the radiator;
• and
• a controller configured to determine a failure of the coolant switching device and stop the on-board charger from charging the vehicle battery, when a temperature of the on-board charger is greater than a first set temperature and a temperature of the electronic device is less than a second set temperature.