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 .