ABNORMAL SIGNAL OUTPUT PREVENTION CIRCUIT, FAILURE DIAGNOSIS SYSTEM, FUEL INJECTION CONTROL DEVICE, AND ABNORMAL SIGNAL OUTPUT PREVENTION METHOD

PROBLEM TO BE SOLVED: To provide an abnormal signal output prevention circuit for improving judgment accuracy by preventing misjudgment in diagnosing failure at a portion related to an ignition system of an internal combustion engine and ion current detection. SOLUTION: This circuit comprises energization disconnection switch means for switching a signal output line SL from a mask circuit 5 from an energization condition to a disconnection condition based on a change of switch signals of a monitor cylinder, a mask circuit MC for holding the disconnection condition of the signal output line SL switched by the energization disconnection switch means for a predetermined condition, a signal monitor circuit SM monitoring output signals from the mask circuit 5 in a disconnection condition holding period, and disconnection continuance judgment means for judging whether the disconnection condition of the signal output line SL is continued or not based on signals obtained from the signal monitor circuit SMC in the disconnection condition holding period. COPYRIGHT: (C)2008,JPO&INPIT