Diagnostic apparatus for catalytic converter of an internal combustion engine

Diagnostic apparatus for catalytic converter of an internal combustion engine, comprising:

• a first air-fuel ratio sensor situated upstream of said catalytic converter relative to a direction of gas flow therein;
• a second air-fuel ratio sensor situated downstream of said catalytic converter relative to said direction of gas flow;
• a deterioration index calculating unit for determining a deterioration index indicative of an extent of deterioration of said catalytic converter in response to output signals from said first and second air-fuel ratio sensors;
• a correction factor calculator for determining a correction factor to adjust said deterioration index to compensate for deviations due to variation of intake air quantity of said engine and a cycling frequency of an output of said downstream air-fuel ratio sensor.

Method of detecting deterioration of a catalytic converter of an internal combustion engine having a fuel input control system and first and second air-fuel ratio sensors arranged upstream and downstream of said catalytic converter respectively, said method comprising the steps of:

• first sensing at least one operating parameter of said engine and providing at least one output signal indicative thereof;
• second detecting when said at least one output signal falls within a predetermined diagnostic area and generating an enabling signal indicative thereof;
• third, during time when said enabling signal is being generated, detecting when an output signal from said second air-fuel ratio sensor falls outside a predetermined range, and adjusting said fuel input control system to shift said output signal of said second air-fuel ratio sensor into said predetermined range;
• fourth, when said output signal of said second air-fuel ratio sensor is within said predetermined range, calculating a deterioration index for said catalytic converter based on output signals of said first and second air-fuel sensors.