A system for determining the effectiveness of a catalytic coating on a radiator in a motor vehicle. The system provides a driver or maintenance staff status of the catalytic function provided by the catalytic coating on a heat exchanger in a cooling system connected to an engine in a motor vehicle. The motor vehicle includes an engine, a cooling circuit, a heat exchanger having at least a partially externally coating of a catalytic material for converting environmentally harmful substances in ambient air. A sensor determines the effectiveness of the catalytic exchanger by comparing a parameter on one side of the heat exchanger with a parameter on the other side of the heat exchanger. The sensor determines the effectiveness of the catalytic exchanger by measuring untreated air and air that is treated by passing through the heat exchanger. A fan is used to reverse the flow of air to and from the heat exchanger. The sensor can also determine the degradation of a test cell which degrades in a similar manner as the catalytic coating on the heat exchanger.