Patent ID: 8249827

Claim:
A method of diagnosing an operating condition of an electrically conductive particulate matter sensor, said sensor comprising a substrate having an electrical resistance that varies with temperature and two electrodes on said substrate adapted to collect particulate matter between the electrodes, thereby establishing an electrically conductive path through collected particulate matter between the electrodes that can be detected by measuring electrical resistance between the electrodes, R elect , said method comprising the steps of: (a) providing heat to the sensor in an amount sufficient to modify the electrical resistance of the substrate, and detecting whether R elect changes in a manner consistent with heating of the substrate; (b) if R elect increases in a manner consistent with heating of the substrate in step (a), then removing the heat provided in step (a) to cool the substrate; (c) if R elect does not change in a manner consistent with heating of the substrate in step (a) or R elect does not change in a manner consistent with cooling of the substrate in step (b), then diagnosing a failure condition for the sensor; and (d) if R elect changes in a manner consistent with cooling of the substrate in step (b), then diagnosing a validation that the sensor is in proper working condition.