A fault detecting apparatus for a gas concentration sensor is provided.
The apparatus includes a storage device and a fault detecting circuit.
The storage device stores therein fault detectable conditions in which
preselected different types of faults of the gas concentration sensor are
allowed to be detected, respectively. The fault detecting circuit works
to detect a selected one of the faults stored in said storage device.
When one of the fault detectable conditions is encountered during
operation of the gas concentration sensor, the fault detecting circuit
initiates detection of a corresponding one of the faults based on an
output of the gas concentration sensor, thereby enabling the fault
detecting circuit to identify the type of one of the faults to be
detected correctly.