Abnormality-detecting device for internal combustion engines

An abnormality-detecting device for an internal combustion engine having an exhaust system, catalytic converter means arranged in said exhaust system, and first and second oxygen concentration-detecting means arranged in said exhaust system at locations upstream and downstream of said catalytic converter means, comprising:

• catalytic converter deterioration-detecting means for detecting a degree of deterioration of said catalytic converter means, based on an output from said second oxygen concentration-detecting means;
• reference value-setting means for setting a reference value for determining an abnormality in said engine, based on the degree of deterioration of said catalytic converter means detected by said catalytic converter deterioration-detecting means;
• abnormality determining means for comparing between said reference value set by said reference value-setting means and a value based on an output from said first oxygen concentration detecting means, and determining the abnormality in said engine, based on a result of said comparison;
• and
• alarming means for issuing an alarm when said abnormality has been detected by said abnormality determining means.