Abstract: A device for detecting the deterioration of a catalyst wherein oxygen sensors are provided on the upstream and downstream sides of the catalytic converter. Circuitry is provided for calculating integration values corresponding to areas surrounded by output signals of the oxygen sensors and designated signals; for calculating time periods between which the sensor signals reverse polarity with respect to the designated signals; for calculating a parameter for determining deterioration of the catalyst based on the integration values, the time periods or a combination of both; for determining deterioration of the catalyst by comparing the calculated parameter with a predetermined value; and for issuing an alarm when the catalyst is determined as deteriorated.

Abstract: A failure diagnosis device for an EGR control system detects a predetermined running condition of the engine, and includes a control device which inputs values of predetermined parameters signifying the running condition of the engine at first predetermined times. The control device calculates differences between preceding input values and current input values, accumulates the differences, and opens the EGR path after determining that the EGR control system is normal, i.e. when the accumulated value reaches or exceeds a predetermined value after a second predetermined time has elapsed from when the EGR path is forcibly closed. The control device determines that the EGR control system has failed and generates an alarm when the accumulated value is below the predetermined value when the second predetermined time has elapsed.

Abstract: A disorder diagnosis device for a combustion engine having a fuel injector for each cylinder and a fuel system for supplying fuel to the injector comprises an air-fuel ratio sensor provided at an exhaust tube of the combustion engine for providing an air-fuel ratio signal indicative of an air-fuel ratio, and a control unit responsive to the air-fuel ratio sensor for calculating a first value by comparing the air-fuel ratio signal with a preset value and for calculating a second value by comparing a signal corresponding to the air-fuel ratio signal with a predetermined value so as to decide if the fuel system is in disorder on the basis of a combination of the first and second values.