Catalytic converter efficiency monitor

A method for monitoring efficiency of a catalytic converter in a motor vehicle having an internal combustion engine, said method comprising the steps:

• operating an engine under a closed loop condition;
• determining if at least one predetermined condition is met for monitoring the efficiency of the catalytic converter;
• determining whether the engine has stabilized if the at least one preestablished condition is met;
• combining a square wave multiplier signal with a feedback multiplier signal if the engine has stabilized;
• counting a number of square wave edges of the combined signal for an upstream oxygen sensor positioned upstream of the catalytic converter;
• counting a number of switches of a signal across a predetermined switch point from a downstream oxygen sensor positioned downstream of the catalytic converter;
• calculating a switching frequency ratio based on the count of the square wave edges and oxygen sensor switches;
• determining if the switching frequency ratio is greater than a predetermined level;
• concluding that the catalytic converter is efficient if the switching frequency ratio is less than the predetermined level;
• and
• concluding that the catalytic converter is not efficient if the switching frequency ratio is greater than the predetermined level.