Patent ID: 6818120
Filing Date: 2004-11-16
Classification: F02D,G01N

Abstract:
An O2-sensor fault diagnosis apparatus comprising:an O2-sensor for detecting concentration of oxygen contained in an exhaust gas of an internal combustion engine; a feedback control portion for controlling a quantity of fuel supplied to the internal combustion engine through feedback control according to an output signal of the O2-sensor; a state judging portion for judging whether the O2-sensor is in an active state or in an inactive state on the basis of a voltage of the output signal of the O2-sensor; and a fault diagnosis portion for diagnosing whether the O2-sensor has any fault on the basis of the voltage of the output signal of the O2-sensor under a condition where it is judged that the O2-sensor is in the inactive state, wherein fuel is not injected when the O2-sensor is in the inactive states, wherein said fault diagnosis portion includes an input resistance changing portion for changing an input resistance so as to cause a change in a level of the output signal of said O2-sensor, and identifies a fault of said O2-sensor on the basis of the change in the level of the output signal caused by changing the input resistance, and wherein said fault diagnosis portion diagnoses whether said O2-sensor has any fault by changing said input resistance each time said state judging portion judges that said O2-sensor is in the inactive state.