Patent ID: 8823400

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) commanding the provision of 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 a contaminant on the substrate; (b) if R elect changes in a manner consistent with heating of a contaminant on the substrate in step (a), then diagnosing a contamination condition for the sensor; wherein said sensor includes a heater element adapted to heat an area between said electrodes, and step (a) comprises the steps of: (1) measuring R elect before activating the heater element and storing the value as R OBD — init ; (2) activating the heater element for a first period of time; while periodically measuring R elect , and storing the value as R OBD —R hot ; (3) comparing R OBD —R hot to a predetermined percentage K R —R OBD —R init ; (4) if R OBD —R hot is not less than the predetermined percentage K R —R OBD —R cont —R pct of R OBD —R init , then determining that R elect did not change in a manner consistent with heating a contaminated substrate; and (5) if R OBD —R hot is less than the predetermined percentage K R —R OBD —R cont —R pct of R OBD —R init as determined in step (3) during said first period of time, then determining that R elect changed in a manner consistent with heating a contaminated substrate.