Abstract: A system for measuring the efficiency of a motor vehicle catalytic converter through which gas flow passes. Two sensors monitor the gas conditions upstream and downstream of the catalytic converter and provide output signals to a microprocessor having dual input channels. The sensors may be lambda sensors. Each input channel leads to integration paths which receive the output from the sensors and calculate a variable average. The variable average is sent sequentially to a difference calculating node, a squaring node, and an integration module. The integration module sums intermediate signals over a period of time and generates output signals. The output signals are compared to each other and to reference values to determine if the catalytic converter is operating efficiently. A method of determining the efficiency of the catalytic converter using the aforementioned system is also provided.