Failure detection apparatus and failure detection method for particulate filter

A failure detection method for a particulate filter installed in an exhaust passage for an internal combustion engine, the method comprising:

• arranging a sensor downstream of the particulate filter, the sensor including
• a particulate matter detection unit configured to allow, on a surface thereof, accumulation of particulate matter contained in exhaust gas having passed through the particulate filter, and output a signal corresponding to an amount of the accumulated particulate matter, and
• a heater unit configured to heat the particulate matter detection unit;
• an output storage step for storing an output value from the sensor as an initial value for next start when or while the internal combustion engine is stopped;
• a start determination step for determining start of the internal combustion engine after the output storage step;
• a dryness determination step for determining whether the exhaust gas contains water droplets while the internal combustion engine is in operation after the next start;
• a heating step for, in response to the exhaust gas being determined to contain no water droplets in the dryness determination step, activating the heater unit to heat the particulate matter detection unit to a first temperature allowing the accumulated particulate matter to remain and moisture included in the particulate matter to be removed;
• and
• a failure determination step for determining whether the particulate filter has a failure based on a difference between the initial value and an output value from the sensor after the heating in the heating step.