Abstract: An apparatus for failure diagnosis starts counting a frequency of a switching action of a foot brake switch when determining that vehicle speed is higher than a first criterion value, and ceases to count the frequency of the switching action when determining that the vehicle speed has decreased below a second criterion value set to be lower than the first criterion value. When the frequency of the switching action counted by a count section is less than a predetermined value, the apparatus for failure diagnosis determines that the foot brake switch has a failure.

Abstract: A filter upstream-side pressure sensor detects the pressure on an upstream side of a filter. A filter downstream-side pressure calculating device subtracts an actual measurement value of the pressure difference between the upstream side and the downstream side of the filter from a pressure value on the upstream side of the filter. Based on this subtraction, the filter downstream-side pressure calculating device calculates a pressure value on the downstream side of the filter. A filter downstream-side pressure estimating device estimates a pressure value on the downstream side of the filter. An abnormality detection device compares the difference between the calculated pressure value and the estimated pressure value with a threshold. If the difference exceeds the threshold, it is determined that at least one of a differential pressure sensor and the filter upstream-side pressure sensor is not working normally.

Abstract: An exhaust purifying apparatus is provided with a filter located in an exhaust path of an internal combustion engine and configured to collect particulates in exhaust gas. The exhaust purifying apparatus is also provided with a differential pressure sensor which detects the pressure difference generated between the upstream side and downstream side of the filter. The problem detection apparatus of the exhaust purifying apparatus is provided with a differential pressure calculation unit and a judgment unit. The differential pressure calculation unit calculates the pressure difference between the upstream and downstream sides of the filter based on the operating state of the internal combustion engine. The judgment unit calculates a difference P between an actual measurement value of the pressure difference and a calculation differential pressure value compares the difference P with a threshold value, and detects that the filter has a problem.

Abstract: An apparatus for failure diagnosis of an intake air flow sensor is provided which, when the operating state of an engine is judged to be in a low flow rate region, determines whether or not the intake air flow rate detected by the intake air flow sensor is excessively high relative to a theoretical intake air flow rate corresponding to the operating state of the engine and, if the detected intake air flow rate is excessively high, judges that the intake air flow sensor has failed. Also, when the operating state of the engine is judged to be in a high flow rate region, the apparatus for failure diagnosis determines whether or not the detected intake air flow rate is excessively low relative to the theoretical intake air flow rate and, if the detected intake air flow rate is excessively low, judges that the intake air flow sensor has failed.

Abstract: An unburned fuel supply section performs temperature rise control to supply fuel to an oxidizing catalyst disposed upstream of an exhaust purification device to cause temperature rise of the exhaust purification device using heat generated in oxidation reaction of fuel on the catalyst. During the temperature rise control, an actual cumulative fuel quantity calculation section obtains actual cumulative fuel quantity by accumulating the amount of fuel supplied to the catalyst. A theoretical cumulative fuel quantity calculation section calculates fuel supply quantity required for temperature rise of the exhaust purification device on the premise that oxidation performance of the catalyst is not deteriorated, and obtains theoretical cumulative fuel quantity by accumulating the calculated fuel supply quantity.